201308140500


C# Tutorial

    http://www.tutorialspoint.com/csharp/index.htm


Contents

  C# Basic Tutorial
    C# Home
    C# - Overview
    C# - Environment
    C# - Program Structure
    C# - Basic Syntax
    C# - Data Types
    C# - Type Conversion
    C# - Variables
    C# - Constants
    C# - Operators
    C# - Decision Making
    C# - Loops
    C# - Encapsulation
    C# - Methods
    C# - Nullables
    C# - Arrays
    C# - Strings
    C# - Struct
    C# - Enums
    C# - Classes
    C# - Inheritance
    C# - Polymorphism
    C# - Operator Overloading
    C# - Interfaces
    C# - Namespaces
    C# - Preprocessor Directives
    C# - Regular Expressions
    C# - Exception Handling
    C# - File I/O


C# Home

C# is a simple, modern, general-purpose, object-oriented programming language developed by Microsoft within its .NET initiative led by Anders Hejlsberg.

This tutorial will teach you basic C# programming and will also take you through various advanced concepts related to C# programming language.


Audience

This tutorial has been prepared for the beginners to help them understand basic C# programming. After completing this tutorial, you will find yourself at a moderate level of expertise in C# programming from where you can take yourself to next levels.


Prerequisites

C# programming is very much based on C and C++ programming languages, so if you have basic understanding on C or C++ programming then it will be a fun to learn C# programming language.


Compile/Execute C# Programs

If you are willing to learn the C# programming with a C# Mono Compiler then you have compileonline.com available on a high end dedicated server giving you real programming experience with a comfort of single click compilation and execution. Yes! it is absolutely free and its online.


1 - C# Quick Reference Guide

A quick C# reference guide for C# Programmers.

C# Quick Reference Guide

  http://www.tutorialspoint.com/csharp/csharp_quick_guide.htm

2 - C# Useful Resources

  http://www.tutorialspoint.com/csharp/csharp_useful_resources.htm

A collection of C# Sites, Books and Articles is given at this page.

3 - C++ Tutorials

  http://www.tutorialspoint.com/cplusplus/index.htm

If you are starting with C++ then it's best place to start with.

4 - C# Tutorial in PDF

  http://www.tutorialspoint.com/csharp/csharp_pdf_version.htm

Download a quick C# tutorial in PDF format.

----------

C# - Overview

C# is a modern, general-purpose, object-oriented programming language developed by Microsoft and approved by Ecma and ISO.

C# was developed by Anders Hejlsberg and his team during the development of .Net Framework.

C# is designed for Common Language Infrastructure (CLI), which consists of the executable code and runtime environment that allows use of various high-level languages to be used on different computer platforms and architectures.

The following reasons make C# a widely used professional language:

    Modern, general-purpose programming language
    Object oriented.
    Component oriented.
    Easy to learn.
    Structured language.
    It produces efficient programs.
    It can be compiled on a variety of computer platforms.
    Part of .Net Framework.


Strong Programming Features of C#

Although C# constructs closely follow traditional high-level languages C and C++ and being an object-oriented programming language, it has strong resemblance with Java, it has numerous strong programming features that make it endearing to multitude of programmers worldwide.

Following is the list of few important features:

    Boolean Conditions
    Automatic Garbage Collection
    Standard Library
    Assembly Versioning
    Properties and Events
    Delegates and Events Management
    Easy-to-use Generics
    Indexers
    Conditional Compilation
    Simple Multithreading
    LINQ and Lambda Expressions
    Integration with Windows

----------

C# - Environment

In this chapter, we will discuss the tools required for creating C# programming. We have already mentioned that C# is part of .Net framework and is used for writing .Net applications. Therefore, before discussing the available tools for running a C# program, let us understand how C# relates to the .Net framework.
The .Net Framework

The .Net framework is a revolutionary platform that helps you to write the following types of applications:

    Windows applications
    Web applications
    Web services

The .Net framework applications are multi-platform applications. The framework has been designed in such a way that it can be used from any of the following languages: C#, C++, Visual Basic, Jscript, COBOL, etc. All these languages can access the framework as well as communicate with each other.

The .Net framework consists of an enormous library of codes used by the client languages like C#. Following are some of the components of the .Net framework:

    Common Language Runtime (CLR)
    The .Net Framework Class Library
    Common Language Specification
    Common Type System
    Metadata and Assemblies
    Windows Forms
    ASP.Net and ASP.Net AJAX
    ADO.Net
    Windows Workflow Foundation (WF)
    Windows Presentation Foundation
    Windows Communication Foundation (WCF)
    LINQ

For the jobs each of these components perform, please see ASP.Net - Introduction, and for details of each component, please consult Microsoft's documentation.
Integrated Development Environment (IDE) For C#

Microsoft provides the following development tools for C# programming:

    Visual Studio 2010 (VS)
    Visual C# 2010 Express (VCE)
    Visual Web Developer

The last two are freely available from Microsoft official website. Using these tools, you can write all kinds of C# programs from simple command-line applications to more complex applications. You can also write C# source code files using a basic text editor, like Notepad, and compile the code into assemblies using the command-line compiler, which is again a part of the .NET Framework.

Visual C# Express and Visual Web Developer Express edition are trimmed down versions of Visual Studio and has the same look and feel. They retain most features of Visual Studio. In this tutorial, we have used Visual C# 2010 Express.

You can download it from Microsoft Visual Studio. It gets automatically installed in your machine. Please note that you need an active internet connection for installing the express edition.
Writing C# Programs on Linux or Mac OS

Although the.NET Framework runs on the Windows operating system, there are some alternative versions that work on other operating systems. Mono is an open-source version of the .NET Framework which includes a C# compiler and runs on several operating systems, including various flavors of Linux and Mac OS. Kindly check Go Mono.

The stated purpose of Mono is not only to be able to run Microsoft .NET applications cross-platform, but also to bring better development tools to Linux developers. Mono can be run on many operating systems including Android, BSD, iOS, Linux, OS X, Windows, Solaris and UNIX.

----------

C# - Program Structure

Before we study basic building blocks of the C# programming language, let us look at a bare minimum C# program structure so that we can take it as a reference in upcoming chapters.


C# Hello World Example

A C# program basically consists of the following parts:

    Namespace declaration
    A class
    Class methods
    Class attributes
    A Main method
    Statements & Expressions
    Comments

Let us look at a simple code that would print the words "Hello World":

  using System;
  namespace HelloWorldApplication
  {
     class HelloWorld
     {
        static void Main(string[] args)
        {
           /* my first program in C# */
           Console.WriteLine("Hello World");
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Hello World

Let us look at various parts of the above program:

  - The first line of the program using System; - the using keyword is used to include the System namespace in the program. A program generally has multiple using statements.
  - The next line has the namespace declaration. A namespace is a collection of classes. The HelloWorldApplication namespace contains the class HelloWorld.
  - The next line has a class declaration, the class HelloWorld contains the data and method definitions that your program uses. Classes generally would contain more than one method. Methods define the behavior of the class. However, the HelloWorld class has only one method Main.
  - The next line defines the Main method, which is the entry point for all C# programs. The Main method states what the class will do when executed
  - The next line /*...*/ will be ignored by the compiler and it has been put to add additional comments in the program.
  - The Main method specifies its behavior with the statement Console.WriteLine("Hello World");
  - WriteLine is a method of the Console class defined in the System namespace. This statement causes the message "Hello, World!" to be displayed on the screen.
  - The last line Console.ReadKey(); is for the VS.NET Users. This makes the program wait for a key press and it prevents the screen from running and closing quickly when the program is launched from Visual Studio .NET.

It's worth to note the following points:

  - C# is case sensitive.
  - All statements and expression must end with a semicolon (;).
  - The program execution starts at the Main method.
  - Unlike Java, file name could be different from the class name.


Compile & Execute a C# Program:

If you are using Visual Studio.Net for compiling and executing C# programs, take the following steps:

  - Start Visual Studio.
  - On the menu bar, choose File, New, Project.
  - Choose Visual C# from templates, and then choose Windows.
  - Choose Console Application.
  - Specify a name for your project, and then choose the OK button.
  - The new project appears in Solution Explorer.
  - Write code in the Code Editor.

    Click the Run button or the F5 key to run the project. A Command Prompt window appears that contains the line Hello World.

You can compile a C# program by using the command-line instead of the Visual Studio IDE:

  - Open a text editor and add the above-mentioned code.
  - Save the file as helloworld.cs
  - Open the command prompt tool and go to the directory where you saved the file.
  - Type csc helloworld.cs and press enter to compile your code.

If there are no errors in your code, the command prompt will take you to the next line and would generate helloworld.exe executable file.

Next, type helloworld to execute your program. You will be able to see "Hello World" printed on the screen.

----------

C# - Basic Syntax

C# is an object-oriented programming language. In Object-Oriented Programming methodology, a program consists of various objects that interact with each other by means of actions. The actions that an object may take are called methods. Objects of the same kind are said to have the same type or, more often, are said to be in the same class.

For example, let us consider a Rectangle object. It has attributes like length and width. Depending upon the design, it may need ways for accepting the values of these attributes, calculating area and display details.

Let us look at an implementation of a Rectangle class and discuss C# basic syntax, on the basis of our observations in it:

  using System;
  namespace RectangleApplication
  {
      class Rectangle
      {
          // member variables
          double length;
          double width;
          public void Acceptdetails()
          {
              length = 4.5;
              width = 3.5;
          }
          public double GetArea()
          {
              return length * width;
          }
          public void Display()
          {
              Console.WriteLine("Length: {0}", length);
              Console.WriteLine("Width: {0}", width);
              Console.WriteLine("Area: {0}", GetArea());
          }
      }

      class ExecuteRectangle
      {
          static void Main(string[] args)
          {
              Rectangle r = new Rectangle();
              r.Acceptdetails();
              r.Display();
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Length: 4.5
  Width: 3.5
  Area: 15.75


The using Keyword

The first statement in any C# program is

  using System;

The using keyword is used for including the namespaces in the program. A program can include multiple using statements.


The class Keyword

The class keyword is used for declaring a class.


Comments in C#

Comments are used for explaining code. Compilers ignore the comment entries. The multiline comments in C# programs start with /* and terminates with the characters */ as shown below:

  /* This program demonstrates
  The basic syntax of C# programming
  Language */

Single-line comments are indicated by the '//' symbol. For example,

  }//end class Rectangle


Member Variables

Variables are attributes or data members of a class, used for storing data. In the preceding program, the Rectangle class has two member variables named length and width.
Member Functions

Functions are set of statements that perform a specific task. The member functions of a class are declared within the class. Our sample class Rectangle contains three member functions: AcceptDetails, GetArea and Display.
Instantiating a Class

In the preceding program, the class ExecuteRectangle is used as a class, which contains the Main() method and instantiates the Rectangle class.
Identifiers

An identifier is a name used to identify a class, variable, function, or any other user-defined item. The basic rules for naming classes in C# are as follows:

  - A name must begin with a letter that could be followed by a sequence of letters, digits (0 - 9) or underscore. The first character in an identifier cannot be a digit.

  - It must not contain any embedded space or symbol like ? - +! @ # % ^ & * ( ) [ ] { } . ; : " ' / and \. However, an underscore ( _ ) can be used.

  - It should not be a C# keyword.


C# Keywords

Keywords are reserved words predefined to the C# compiler. These keywords cannot be used as identifiers; however, if you want to use these keywords as identifiers, you may prefix the keyword with the @ character.

In C#, some identifiers have special meaning in context of code, such as get and set, these are called contextual keywords.

The following table lists the reserved keywords and contextual keywords in C#:

Reserved Keywords

  +------------+------------+------------+------------+------------+
  | abstract   | as         | base       | bool       | break      |
  | byte       | case       | catch      | char       | checked    |
  | class      | const      | continue   | decimal    | default    |
  | delegate   | do         | double     | else       | enum       |
  | event      | explicit   | extern     | false      | finally    |
  | fixed      | float      | for        | foreach    | goto       |
  | if         | implicit   | in         | in g.m.*   | int        |
  | interface  | internal   | is         | lock       | long       |
  | namespace  | new        | null       | object     | operator   |
  | out        | out        | g.m.*      | override   | params     |
  | private    | protected  | public     | readonly   | ref        |
  | return     | sbyte      | sealed     | short      | sizeof     |
  | stackalloc | static     | string     | struct     | switch     |
  | this       | throw      | true       | try        | typeof     |
  | uint       | ulong      | unchecked  | unsafe     | ushort     |
  | using      | virtual    | void       | volatile   | while      |
  +------------+------------+------------+------------+------------+

*) g.m -- global modifier

Contextual Keywords

  +------------+------------+------------+------------+------------+
  | add        | alias      | ascending  | descending | dynamic    |
  | from       | get        | global     | group      | into       |
  | join       | let        | orderby    | p*(type)   | p*(method) |
  | remove     | select     | set        |            |            |
  +------------+------------+------------+------------+------------+

*) p - partial

----------

C# - Data Types

In C#, variables are categorized into the following types:

    Value types
    Reference types
    Pointer types


Value Types

Value type variables can be assigned a value directly. They are derived from the class System.ValueType.

The value types directly contain data. Some examples are int, char, float, which stores numbers, alphabets, floating point numbers, respectively. When you declare an int type, the system allocates memory to store the value.

The following table lists the available value types in C# 2010:

  +---------+--------------------------------+---------------------------+---------+
  | Type    | Represents                     | Range                     | Default |
  +---------+--------------------------------+---------------------------+---------+
  | bool    | Boolean value                  | True or False             | False   |
  +---------+--------------------------------+---------------------------+---------+
  | byte    | 8-bit unsigned integer         | 0 to 255                  | 0       |
  +---------+--------------------------------+---------------------------+---------+
  | char    | 16-bit Unicode character       | U +0000 to U +ffff        | '\0'    |
  +---------+--------------------------------+---------------------------+---------+
  | decimal | 128-bit precise decimal values | (-7.9x10^28 to 7.9x10^28) | 0.0M    |
  |         | with 28-29 significant digits  | / 10^0 to 28              |         |
  +---------+--------------------------------+---------------------------+---------+
  | double  | 64-bit double-precision        | (+/-)5.0x10^-324 to       | 0.0D    |
  |         | floating point type            | (+/-)1.7 x 10^308         |         |
  +---------+--------------------------------+---------------------------+---------+
  | float   | 32-bit single-precision        | -3.4x10^38 to +3.4x10^38  | 0.0F    |
  |         | floating point type            |                           |         |
  +---------+--------------------------------+---------------------------+---------+
  | int     | 32-bit signed integer type     | -2,147,483,648 to         | 0       |
  |         |                                | 2,147,483,647             |         |
  +---------+--------------------------------+---------------------------+---------+
  | long    | 64-bit signed integer type     | -923,372,036,854,775,808  | 0L      |
  |         |                                | 9,223,372,036,854,775,807 |         |
  +---------+--------------------------------+---------------------------+---------+
  | sbyte   | 8-bit signed integer type      | -128 to 127               | 0       |
  +---------+--------------------------------+---------------------------+---------+
  | short   | 16-bit signed integer type     | -32,768 to 32,767         | 0       |
  +---------+--------------------------------+---------------------------+---------+
  | uint    | 32-bit unsigned integer type   | 0 to 4,294,967,295        | 0       |
  +---------+--------------------------------+---------------------------+---------+
  | ulong   | 64-bit unsigned integer type   | 0 to                      | 0       |
  |         |                                | 18,446,744,073,709,551,615|         |
  +---------+--------------------------------+---------------------------+---------+
  | ushort  | 16-bit unsigned integer type   | 0 to 65,535               | 0       |
  +---------+--------------------------------+---------------------------+---------+

To get the exact size of a type or a variable on a particular platform, you can use the sizeof method. The expression sizeof(type) yields the storage size of the object or type in bytes. Following is an example to get the size of int type on any machine:

  namespace DataTypeApplication
  {
     class Program
     {
        static void Main(string[] args)
        {
           Console.WriteLine("Size of int: {0}", sizeof(int));
           Console.ReadLine();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Size of int: 4


Reference Types

The reference types do not contain the actual data stored in a variable, but they contain a reference to the variables.

In other words, they refer to a memory location. Using more than one variable, the reference types can refer to a memory location. If the data in the memory location is changed by one of the variables, the other variable automatically reflects this change in value. Example of built-in reference types are: object, dynamic and string.


Object Type

The Object Type is the ultimate base class for all data types in C# Common Type System (CTS). Object is an alias for System.Object class. So object types can be assigned values of any other types, value types, reference types, predefined or user-defined types. However, before assigning values, it needs type conversion.

When a value type is converted to object type, it is called boxing and on the other hand, when an object type is converted to a value type, it is called unboxing.

  object obj;
  obj = 100; // this is boxing


Dynamic Type

You can store any type of value in the dynamic data type variable. Type checking for these types of variables takes place at run-time.

Syntax for declaring a dynamic type is:

  dynamic <variable_name> = value;

For example,

  dynamic d = 20;

Dynamic types are similar to object types except that type checking for object type variables takes place at compile time, whereas that for the dynamic type variables take place at run time.


String Type

The String Type allows you to assign any string values to a variable. The string type is an alias for the System.String class. It is derived from object type. The value for a string type can be assigned using string literals in two forms: quoted and @quoted.

For example,

  String str = "Tutorials Point";

A @quoted string literal looks like:

  @"Tutorials Point";

The user-defined reference types are: class, interface, or delegate. We will discuss these types in later chapter.


Pointer Types

Pointer type variables store the memory address of another type. Pointers in C# have the same capabilities as in C or C++.

Syntax for declaring a pointer type is:

  type* identifier;

For example,

  char* cptr;
  int*  iptr;

We will discuss pointer types in the chapter 'Unsafe Codes'.

----------

C# - Type Conversion

Type conversion is basically type casting or converting one type of data to another type. In C#, type casting has two forms:

  - Implicit type conversion - these conversions are performed by C# in a type-safe manner. Examples are conversions from smaller to larger integral types and conversions from derived classes to base classes.

  - Explicit type conversion - these conversions are done explicitly by users using the pre-defined functions. Explicit conversions require a cast operator.

The following example shows an explicit type conversion:

  namespace TypeConversionApplication
  {
      class ExplicitConversion
      {
          static void Main(string[] args)
          {
              double d = 5673.74;
              int i;

              // cast double to int.
              i = (int)d;
              Console.WriteLine(i);
              Console.ReadKey();

          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  5673


C# Type Conversion Methods

C# provides the following built-in type conversion methods:

  +-----+------------+-------------------------------------------------+
  | S.N | Methods    | Description                                     |
  +-----+------------+-------------------------------------------------+
  | 1   | ToBoolean  | Converts a type to a Boolean value, where       |
  |     |            | possible.                                       |
  +-----+------------+-------------------------------------------------+
  | 2   | ToByte     | Converts a type to a byte.                      |
  +-----+------------+-------------------------------------------------+
  | 3   | ToChar     | Converts a type to a single Unicode character,  |
  |     |            | where possible.                                 |
  +-----+------------+-------------------------------------------------+
  | 4   | ToDateTime | Converts a type (integer or string type) to     |
  |     |            | date-time structures.                           |
  +-----+------------+-------------------------------------------------+
  | 5   | ToDecimal  | Converts a floating point or integer type to a  |
  |     |            | decimal type.                                   |
  +-----+------------+-------------------------------------------------+
  | 6   | ToDouble   | Converts a type to a double type.               |
  +-----+------------+-------------------------------------------------+
  | 7   | ToInt16    | Converts a type to a 16-bit integer.            |
  +-----+------------+-------------------------------------------------+
  | 8   | ToInt32    | Converts a type to a 32-bit integer.            |
  +-----+------------+-------------------------------------------------+
  | 9   | ToInt64    | Converts a type to a 64-bit integer.            |
  +-----+------------+-------------------------------------------------+
  | 10  | ToSbyte    | Converts a type to a signed byte type.          |
  +-----+------------+-------------------------------------------------+
  | 11  | ToSingle   | Converts a type to a small floating point number|
  +-----+------------+-------------------------------------------------+
  | 12  | ToString   | Converts a type to a string.                    |
  +-----+------------+-------------------------------------------------+
  | 13  | ToType     | Converts a type to a specified type.            |
  +-----+------------+-------------------------------------------------+
  | 14  | ToUInt16   | Converts a type to an unsigned int type.        |
  +-----+------------+-------------------------------------------------+
  | 15  | ToUInt32   | Converts a type to an unsigned long type.       |
  +-----+------------+-------------------------------------------------+
  | 16  | ToUInt64   | Converts a type to an unsigned big integer.     |
  +-----+------------+-------------------------------------------------+

The following example converts various value types to string type:

  namespace TypeConversionApplication
  {
      class StringConversion
      {
          static void Main(string[] args)
          {
              int i = 75;
              float f = 53.005f;
              double d = 2345.7652;
              bool b = true;

              Console.WriteLine(i.ToString());
              Console.WriteLine(f.ToString());
              Console.WriteLine(d.ToString());
              Console.WriteLine(b.ToString());
              Console.ReadKey();

          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  75
  53.005
  2345.7652
  True

----------

C# - Variables

A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C# has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable.

We have already discussed various data types. The basic value types provided in C# can be categorized as:

  +----------------------+---------------------------------------------+
  | Type                 | Example                                     |
  +----------------------+---------------------------------------------+
  | Integral types       | sbyte, byte, short, ushort, int, uint,      |
  |                      | long, ulong and char                        |
  +----------------------+---------------------------------------------+
  | Floating point types | float and double                            |
  +----------------------+---------------------------------------------+
  | Decimal types        | decimal                                     |
  +----------------------+---------------------------------------------+
  | Boolean types        | true or false values, as assigned           |
  +----------------------+---------------------------------------------+
  | Nullable types       | Nullable data types                         |
  +----------------------+---------------------------------------------+

C# also allows defining other value types of variable like enum and reference types of variables like class, which we will cover in subsequent chapters. For this chapter, let us study only basic variable types.


Variable Definition in C#

Syntax for variable definition in C# is:

  <data_type> <variable_list>;

Here, data_type must be a valid C# data type including char, int, float, double, or any user-defined data type, etc., and variable_list may consist of one or more identifier names separated by commas.

Some valid variable definitions are shown here:

  int i, j, k;
  char c, ch;
  float f, salary;
  double d;

You can initialize a variable at the time of definition as:

  int i = 100;


Variable Initialization in C#

Variables are initialized (assigned a value) with an equal sign followed by a constant expression. The general form of initialization is:

  variable_name = value;

Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as:

  <data_type> <variable_name> = value;

Some examples are:

  int d = 3, f = 5;    /* initializing d and f. */
  byte z = 22;         /* initializes z. */
  double pi = 3.14159; /* declares an approximation of pi. */
  char x = 'x';        /* the variable x has the value 'x'. */

It is a good programming practice to initialize variables properly, otherwise sometimes program would produce unexpected result.

Try the following example which makes use of various types of variables:

  namespace VariableDefinition
  {
      class Program
      {
          static void Main(string[] args)
          {
              short a;
              int b ;
              double c;

              /* actual initialization */
              a = 10;
              b = 20;
              c = a + b;
              Console.WriteLine("a = {0}, b = {1}, c = {2}", a, b, c);
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  a = 10, b = 20, c = 30


Accepting Values from User

The Console class in the System namespace provides a function ReadLine() for accepting input from the user and store it into a variable.

For example,

  int num;
  num = Convert.ToInt32(Console.ReadLine());

The function Convert.ToInt32() converts the data entered by the user to int data type, because Console.ReadLine() accepts the data in string format.


Lvalues and Rvalues in C#:

There are two kinds of expressions in C#:

  - lvalue: An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment.

  - rvalue: An expression that is an rvalue may appear on the right- but not left-hand side of an assignment.

Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement:

  int g = 20;

But following is not a valid statement and would generate compile-time error:

  10 = 20;

----------

C# - Constants and Literals

The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well.

The constants are treated just like regular variables except that their values cannot be modified after their definition.


Integer Literals

An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and no prefix id required for decimal.

An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order.

Here are some examples of integer literals:

  212         /* Legal */
  215u        /* Legal */
  0xFeeL      /* Legal */
  078         /* Illegal: 8 is not an octal digit */
  032UU       /* Illegal: cannot repeat a suffix */

Following are other examples of various types of Integer literals:

  85         /* decimal */
  0213       /* octal */
  0x4b       /* hexadecimal */
  30         /* int */
  30u        /* unsigned int */
  30l        /* long */
  30ul       /* unsigned long */


Floating-point Literals

A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form.

Here are some examples of floating-point literals:

  3.14159       /* Legal */
  314159E-5L    /* Legal */
  510E          /* Illegal: incomplete exponent */
  210f          /* Illegal: no decimal or exponent */
  .e55          /* Illegal: missing integer or fraction */

While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E.
Character Constants

Character literals are enclosed in single quotes, e.g., 'x' and can be stored in a simple variable of char type. A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0').

There are certain characters in C# when they are preceded by a backslash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here, you have a list of some of such escape sequence codes:

  +-----------------+--------------------------------------------------+
  | Escape sequence | Meaning                                          |
  | \\              | \ character                                      |
  | \'              | ' character                                      |
  | \"              | " character                                      |
  | \?              | ? character                                      |
  | \a              | Alert or bell                                    |
  | \b              | Backspace                                        |
  | \f              | Form feed                                        |
  | \n              | Newline                                          |
  | \r              | Carriage return                                  |
  | \t              | Horizontal tab                                   |
  | \v              | Vertical tab                                     |
  | \ooo            | Octal number of one to three digits              |
  | \xhh . . .      | Hexadecimal number of one or more digits         |
  +-----------------+--------------------------------------------------+

Following is the example to show few escape sequence characters:

  namespace EscapeChar
  {
      class Program
      {
          static void Main(string[] args)
          {
              Console.WriteLine("Hello\tWorld\n\n");
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Hello   World


String Literals

String literals or constants are enclosed in double quotes "" or with @"". A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters.

You can break a long line into multiple lines using string literals and separating the parts using whitespaces.

Here are some examples of string literals. All the three forms are identical strings.

  "hello, dear"
  "hello, \
  dear"
  "hello, " "d" "ear"
  @"hello dear"


Defining Constants

Constants are defined using the const keyword. Syntax for defining a constant is:

  const <data_type> <constant_name> = value;

The following program demonstrates defining and using a constant in your program:

  using System;

  namespace DeclaringConstants
  {
      class Program
      {
          static void Main(string[] args)
          {
              const double pi = 3.14159; // constant declaration
              double r;
              Console.WriteLine("Enter Radius: ");
              r = Convert.ToDouble(Console.ReadLine());
              double areaCircle = pi * r * r;
              Console.WriteLine("Radius: {0}, Area: {1}", r, areaCircle);
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Enter Radius:
  3
  Radius: 3, Area: 28.27431

----------

C# - Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C# is rich in built-in operators and provides the following type of operators:

  - Arithmetic Operators
  - Relational Operators
  - Logical Operators
  - Bitwise Operators
  - Assignment Operators
  - Misc Operators

This tutorial will explain the arithmetic, relational, logical, bitwise, assignment and other operators one by one.


Arithmetic Operators

Following table shows all the arithmetic operators supported by C#. Assume variable A holds 10 and variable B holds 20 then:

  +----------+--------------------------------+------------------------+
  | Operator | Description                    | Example                |
  +----------+--------------------------------+------------------------+
  |    +     | Adds two operands              | A + B will give 30     |
  +----------+--------------------------------+------------------------+
  |    -     | Subtracts second operand from  | A - B will give -10    |
  |          | the first                      |                        |
  +----------+--------------------------------+------------------------+
  |    *     | Multiplies both operands       | A * B will give 200    |
  +----------+--------------------------------+------------------------+
  |    /     | Divides numerator by           | B / A will give 2      |
  |          | de-numerator                   |                        |
  +----------+--------------------------------+------------------------+
  |    %     | Modulus Operator and remainder | B % A will give 0      |
  |          | of after an integer division   |                        |
  +----------+--------------------------------+------------------------+
  |    ++    | Increment operator increases   | A++ will give 11       |
  |          | integer value by one           |                        |
  +----------+--------------------------------+------------------------+
  |    --    | Decrement operator decreases   | A-- will give 9        |
  |          | integer value by one           |                        |
  +----------+--------------------------------+------------------------+

Example

Try the following example to understand all the arithmetic operators available in C#:

  using System;

  namespace OperatorsAppl
  {
      class Program
      {
          static void Main(string[] args)
          {
              int a = 21;
              int b = 10;
              int c;

              c = a + b;
              Console.WriteLine("Line 1 - Value of c is {0}", c);
              c = a - b;
              Console.WriteLine("Line 2 - Value of c is {0}", c);
              c = a * b;
              Console.WriteLine("Line 3 - Value of c is {0}", c);
              c = a / b;
              Console.WriteLine("Line 4 - Value of c is {0}", c);
              c = a % b;
              Console.WriteLine("Line 5 - Value of c is {0}", c);
              c = a++;
              Console.WriteLine("Line 6 - Value of c is {0}", c);
              c = a--;
              Console.WriteLine("Line 7 - Value of c is {0}", c);
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Line 1 - Value of c is 31
  Line 2 - Value of c is 11
  Line 3 - Value of c is 210
  Line 4 - Value of c is 2
  Line 5 - Value of c is 1
  Line 6 - Value of c is 21
  Line 7 - Value of c is 22


Relational Operators

Following table shows all the relational operators supported by C#. Assume variable A holds 10 and variable B holds 20, then:

  +----------+---------------------------------+-----------------------+
  | Operator | Description                     | Example               |
  +----------+---------------------------------+-----------------------+
  |   ==     | Checks if the values of two     | (A == B) is not true. |
  |          | operands are equal or not, if   |                       |
  |          | yes then condition becomes true.|                       |
  +----------+---------------------------------+-----------------------+
  |   !=     | Checks if the values of two     | (A != B) is true.     |
  |          | operands are equal or not, if   |                       |
  |          | values are not equal then       |                       |
  |          | condition becomes true.         |                       |
  +----------+---------------------------------+-----------------------+
  |   >      | Checks if the value of left     | (A > B) is not true.  |
  |          | operand is greater than the     |                       |
  |          | value of right operand, if yes  |                       |
  |          | then condition becomes true.    |                       |
  +----------+---------------------------------+-----------------------+
  |   <      | Checks if the value of left     | (A < B) is true.      |
  |          | operand is less than the value  |                       |
  |          | of right operand, if yes then   |                       |
  |          | condition becomes true.         |                       |
  +----------+---------------------------------+-----------------------+
  |   >=     | Checks if the value of left     | (A >= B) is not true. |
  |          | operand is greater than or equal|                       |
  |          | to the value of right operand,  |                       |
  |          | if yes then condition becomes   |                       |
  |          | true.                           |                       |
  +----------+---------------------------------+-----------------------+
  |   <=     | Checks if the value of left     | (A <= B) is true.     |
  |          | operand is less than or equal to|                       |
  |          | the value of right operand, if  |                       |
  |          | yes then condition becomes true.|                       |
  +----------+---------------------------------+-----------------------+

Example

Try the following example to understand all the relational operators available in C#:

  using System;

  class Program
  {
    static void Main(string[] args)
    {
        int a = 21;
        int b = 10;

        if (a == b)
        {
            Console.WriteLine("Line 1 - a is equal to b");
        }
        else
        {
            Console.WriteLine("Line 1 - a is not equal to b");
        }
        if (a < b)
        {
            Console.WriteLine("Line 2 - a is less than b");
        }
        else
        {
            Console.WriteLine("Line 2 - a is not less than b");
        }
        if (a > b)
        {
            Console.WriteLine("Line 3 - a is greater than b");
        }
        else
        {
            Console.WriteLine("Line 3 - a is not greater than b");
        }
        /* Lets change value of a and b */
        a = 5;
        b = 20;
        if (a <= b)
        {
           Console.WriteLine("Line 4 - a is either less than or equal to  b");
        }
        if (b >= a)
        {
           Console.WriteLine("Line 5-b is either greater than or equal to b");
        }
    }
  }

When the above code is compiled and executed, it produces the following result:

  Line 1 - a is not equal to b
  Line 2 - a is not less than b
  Line 3 - a is greater than b
  Line 4 - a is either less than or equal to b
  Line 5 - b is either greater than or equal to b


Logical Operators

Following table shows all the logical operators supported by C#. Assume variable A holds Boolean value true and variable B holds Boolean value false, then:

  +----------+---------------------------------------------------------+
  | Operator | Description                                             |
  |          | Example                                                 |
  +----------+---------------------------------------------------------+
  | &&       | Called Logical AND operator. If both the operands are   |
  |          | non zero then condition becomes true. |                 |
  |          |                                                         |
  |          | (A && B) is false.                                      |
  +----------+---------------------------------------------------------+
  | ||       | Called Logical OR Operator. If any of the two operands  |
  |          | is non zero then condition becomes true.                |
  |          |                                                         |
  |          | (A || B) is true.                                       |
  +----------+---------------------------------------------------------+
  | !        | Called Logical NOT Operator. Use to reverses the        |
  |          | logical state of its operand. If a condition is true    |
  |          | then Logical NOT operator will make false.              |
  |          |                                                         |
  |          | !(A && B) is true.                                      |
  +----------+---------------------------------------------------------+

Example

Try the following example to understand all the logical operators available in C#:

  using System;

  namespace OperatorsAppl
  {
      class Program
      {
          static void Main(string[] args)
          {
              bool a = true;
              bool b = true;

              if (a && b)
              {
                 Console.WriteLine("Line 1 - Condition is true");
              }
              if (a || b)
              {
                  Console.WriteLine("Line 2 - Condition is true");
              }
              /* lets change the value of  a and b */
              a = false;
              b = true;
              if (a && b)
              {
                  Console.WriteLine("Line 3 - Condition is true");
              }
              else
              {
                  Console.WriteLine("Line 3 - Condition is not true");
              }
              if (!(a && b))
              {
                  Console.WriteLine("Line 4 - Condition is true");
              }
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Line 1 - Condition is true
  Line 2 - Condition is true
  Line 3 - Condition is not true
  Line 4 - Condition is true


Bitwise Operators

Bitwise operator works on bits and perform bit by bit operation. The truth tables for &, |, and ^ are as follows:

  +---+---+-------+-------+-------+
  | p | q | p & q | p | q | p ^ q |
  +---+---+-------+-------+-------+
  | 0 | 0 | 0     | 0     | 0     |
  | 0 | 1 | 0     | 1     | 1     |
  | 1 | 1 | 1     | 1     | 0     |
  | 1 | 0 | 0     | 1     | 1     |
  +---+---+-------+-------+-------+

Assume if A = 60; and B = 13; now in binary format they will be as follows:

  A = 0011 1100
  B = 0000 1101

  -----------------

  A&B = 0000 1100
  A|B = 0011 1101
  A^B = 0011 0001
  ~A  = 1100 0011

The Bitwise operators supported by C# are listed in the following table. Assume variable A holds 60 and variable B holds 13 then:

  +----------+---------------------------------+-----------------------+
  | Operator | Description                     | Example               |
  +----------+---------------------------------+-----------------------+
  |    &     | Binary AND Operator copies a    | (A & B) will give 12. |
  |          | bit to the result if it         | which is 0000 1100    |
  |          | exists in both operands.        |                       |
  +----------+---------------------------------+-----------------------+
  |    |     | Binary OR Operator copies a bit | (A | B) will give 61, |
  |          | if it exists in either operand. | which is 0011 1101    |
  +----------+---------------------------------+-----------------------+
  |    ^     | Binary XOR Operator copies the  | (A ^ B) will give 49, |
  |          | bit if it is set in one operand | which is 0011 0001    |
  |          | but not both.                   |                       |
  +----------+---------------------------------+-----------------------+
  |    ~     | Binary Ones Complement Operator | (~A ) will give -61,  |
  |          | is unary and has the effect of  | which is 1100 0011 in |
  |          | 'flipping' bits.                | 2's complement due to |
  |          |                                 | a signed binary number|
  +----------+---------------------------------+-----------------------+
  |    <<    | Binary Left Shift Operator. The | A << 2 will give 240, |
  |          | left operands value is moved    | which is 1111 0000    |
  |          | left by the number of bits      | specified by the right|
  |          |                                 | operand.              |
  +----------+---------------------------------+-----------------------+
  |    >>    | Binary Right Shift Operator.    | A >> 2 will give 15,  |
  |          | The left operands value is moved| which is 0000 1111    |
  |          | right by the number of bits     |                       |
  |          | specified by the right operand. |                       |
  +----------+---------------------------------+-----------------------+

Example

Try the following example to understand all the bitwise operators available in C#:

  using System;
  namespace OperatorsAppl
  {
      class Program
      {
          static void Main(string[] args)
          {
              int a = 60;           /* 60 = 0011 1100 */
              int b = 13;           /* 13 = 0000 1101 */
              int c = 0;

              c = a & b;            /* 12 = 0000 1100 */
              Console.WriteLine("Line 1 - Value of c is {0}", c );

              c = a | b;            /* 61 = 0011 1101 */
              Console.WriteLine("Line 2 - Value of c is {0}", c);

              c = a ^ b;            /* 49 = 0011 0001 */
              Console.WriteLine("Line 3 - Value of c is {0}", c);

              c = ~a;               /*-61 = 1100 0011 */
              Console.WriteLine("Line 4 - Value of c is {0}", c);

              c = a << 2;           /* 240 = 1111 0000 */
              Console.WriteLine("Line 5 - Value of c is {0}", c);

              c = a >> 2;           /* 15 = 0000 1111 */
              Console.WriteLine("Line 6 - Value of c is {0}", c);
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Line 1 - Value of c is 12
  Line 2 - Value of c is 61
  Line 3 - Value of c is 49
  Line 4 - Value of c is -61
  Line 5 - Value of c is 240
  Line 6 - Value of c is 15


Assignment Operators

There are following assignment operators supported by C#:

  +----------+-----------------------------+---------------------------+
  | Operator | Description                 | Example                   |
  +----------+-----------------------------+---------------------------+
  |    =     | Simple assignment operator, | C = A + B will assign     |
  |          | Assigns values from right   | value of A + B into C     |
  |          | side operands to left side  |                           |
  |          | operand                     |                           |
  +----------+-----------------------------+---------------------------+
  |    +=    | Add AND assignment operator,| C += A is equivalent to   |
  |          | It adds right operand to the| C = C + A                 |
  |          | left operand and assign the |                           |
  |          | result to left operand      |                           |
  +----------+-----------------------------+---------------------------+
  |    -=    | Subtract AND assignment     | C -= A is equivalent to   |
  |          | operator, It subtracts right| C = C - A                 |
  |          | operand from the left       |                           |
  |          | operand and assign the      |                           |
  |          | result to left operand      |                           |
  +----------+-----------------------------+---------------------------+
  |    *=    | Multiply AND assignment     | C *= A is equivalent to   |
  |          | operator, It multiplies     | C = C * A                 |
  |          | right operand with the left |                           |
  |          | operand and assign the      |                           |
  |          | result to left operand      |                           |
  +----------+-----------------------------+---------------------------+
  |    /=    | Divide AND assignment       | C /= A is equivalent to   |
  |          | operator, It divides left   | C = C / A                 |
  |          | operand with the right      |                           |
  |          | operand and assign the      |                           |
  |          | result to left operand      |                           |
  +----------+-----------------------------+---------------------------+
  |    %=    | Modulus AND assignment      | C %= A is equivalent to   |
  |          | operator, It takes modulus  | C = C % A                 |
  |          | using two operands and      |                           |
  |          | assign the result to left   |                           |
  |          | operand                     |                           |
  +----------+-----------------------------+---------------------------+
  |   <<=    | Left shift AND assignment   | C <<= 2 is same as        |
  |          | operator                    | C = C << 2                |
  +----------+-----------------------------+---------------------------+
  |   >>=    | Right shift AND assignment  | C >>= 2 is same as        |
  |          | operator                    | C = C >> 2                |
  +----------+-----------------------------+---------------------------+
  |   &=     | Bitwise AND assignment      | C &= 2 is same as         |
  |          | operator                    | C = C & 2                 |
  +----------+-----------------------------+---------------------------+
  |   ^=     | bitwise exclusive OR and    | C ^= 2 is same as         |
  |          | assignment operator         | C = C ^ 2                 |
  +----------+-----------------------------+---------------------------+
  |   |=     | bitwise inclusive OR and    | C |= 2 is same as         |
  |          | assignment operator         | C = C | 2                 |
  +----------+-----------------------------+---------------------------+

Example

Try the following example to understand all the assignment operators available in C#:

  using System;

  namespace OperatorsAppl
  {
      class Program
      {
          static void Main(string[] args)
          {
              int a = 21;
              int c;

              c = a;
              Console.WriteLine("Line 1 - =  Value of c = {0}", c);

              c += a;
              Console.WriteLine("Line 2 - += Value of c = {0}", c);

              c -= a;
              Console.WriteLine("Line 3 - -=  Value of c = {0}", c);

              c *= a;
              Console.WriteLine("Line 4 - *=  Value of c = {0}", c);

              c /= a;
              Console.WriteLine("Line 5 - /=  Value of c = {0}", c);

              c = 200;
              c %= a;
              Console.WriteLine("Line 6 - %=  Value of c = {0}", c);

              c <<= 2;
              Console.WriteLine("Line 7 - <<=  Value of c = {0}", c);

              c >>= 2;
              Console.WriteLine("Line 8 - >>=  Value of c = {0}", c);

              c &= 2;
              Console.WriteLine("Line 9 - &=  Value of c = {0}", c);

              c ^= 2;
              Console.WriteLine("Line 10 - ^=  Value of c = {0}", c);

              c |= 2;
              Console.WriteLine("Line 11 - |=  Value of c = {0}", c);
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Line 1 - =     Value of c = 21
  Line 2 - +=    Value of c = 42
  Line 3 - -=    Value of c = 21
  Line 4 - *=    Value of c = 441
  Line 5 - /=    Value of c = 21
  Line 6 - %=    Value of c = 11
  Line 7 - <<=    Value of c = 44
  Line 8 - >>=    Value of c = 11
  Line 9 - &=    Value of c = 2
  Line 10 - ^=    Value of c = 0
  Line 11 - |=    Value of c = 2


Misc Operators

There are few other important operators including sizeof, typeof and ? : supported by C#.

  +----------+---------------------------------+-----------------------+
  | Operator | Description                     | Example               |
  | sizeof() | Returns the size of a data type | sizeof(int),          |
  |          |                                 | will return 4.        |
  +----------+---------------------------------+-----------------------+
  | typeof() | Returns the type of a class.    | typeof(StreamReader); |
  +----------+---------------------------------+-----------------------+
  | &        | Returns the address of an       | &a; will give actual  |
  |          | variable.                       | address of the        |
  |          |                                 | variable.             |
  +----------+---------------------------------+-----------------------+
  | *        | Pointer to a variable.          | *a; will pointer to a |
  |          |                                 | variable.             |
  +----------+---------------------------------+-----------------------+
  | ? :      | Conditional Expression          | If Condition is true ?|
  |          |                                 | Then value X :        |
  |          |                                 | Otherwise value Y     |
  +----------+---------------------------------+-----------------------+
  | is       | Determines whether an object is | If( Ford is Car)      |
  |          | of a certain type.              | // checks if Ford is  |
  |          |                                 | an object of the Car  |
  |          |                                 | class.                |
  +----------+---------------------------------+-----------------------+
  | as       | Cast without raising an         | Object obj = new      |
  |          | exception if the cast fails.    | StringReader("Hello");|
  |          |                                 | StringReader r =      |
  |          |                                 | obj as StringReader;  |
  +----------+---------------------------------+-----------------------+

Example

  using System;

  namespace OperatorsAppl
  {

     class Program
     {
        static void Main(string[] args)
        {

           /* example of sizeof operator */
           Console.WriteLine("The size of int is {0}", sizeof(int));
           Console.WriteLine("The size of short is {0}", sizeof(short));
           Console.WriteLine("The size of double is {0}", sizeof(double));

           /* example of ternary operator */
           int a, b;
           a = 10;
           b = (a == 1) ? 20 : 30;
           Console.WriteLine("Value of b is {0}", b);

           b = (a == 10) ? 20 : 30;
           Console.WriteLine("Value of b is {0}", b);
           Console.ReadLine();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

The size of int is 4
The size of short is 2
The size of double is 8
Value of b is 30
Value of b is 20


Operators Precedence in C#

Operator precedence determines the grouping of terms in an expression. This affects how an expression is evaluated. Certain operators have higher precedence than others; for example, the multiplication operator has higher precedence than the addition operator:

For example x = 7 + 3 * 2; here, x is assigned 13, not 20 because operator * has higher precedence than +, so it first gets multiplied with 3*2 and then adds into 7.

Here, operators with the highest precedence appear at the top of the table, those with the lowest appear at the bottom. Within an expression, higher precedence operators will be evaluated first.

  +----------------+-----------------------------------+---------------+
  | Category       | Operator                          | Associativity |
  +----------------+-----------------------------------+---------------+
  | Postfix        | () [] -> . ++ - -                 | Left to right |
  | Unary          | + - ! ~ ++ - - (type)* & sizeof   | Right to left |
  | Multiplicative | * / %                             | Left to right |
  | Additive       | + -                               | Left to right |
  | Shift          | << >>                             | Left to right |
  | Relational     | < <= > >=                         | Left to right |
  | Equality       | == !=                             | Left to right |
  | Bitwise AND    | &                                 | Left to right |
  | Bitwise XOR    | ^                                 | Left to right |
  | Bitwise OR     | |                                 | Left to right |
  | Logical AND    | &&                                | Left to right |
  | Logical OR     | ||                                | Left to right |
  | Conditional    | ?:                                | Right to left |
  | Assignment     | = += -= *= /= %=>>= <<= &= ^= |=  | Right to left |
  | Comma          | ,                                 | Left to right |
  +----------------+-----------------------------------+---------------+

Example

  using System;

  namespace OperatorsAppl
  {

     class Program
     {
        static void Main(string[] args)
        {
           int a = 20;
           int b = 10;
           int c = 15;
           int d = 5;
           int e;
           e = (a + b) * c / d;     // ( 30 * 15 ) / 5
           Console.WriteLine("Value of (a + b) * c / d is : {0}", e);

           e = ((a + b) * c) / d;   // (30 * 15 ) / 5
           Console.WriteLine("Value of ((a + b) * c) / d is  : {0}", e);

           e = (a + b) * (c / d);   // (30) * (15/5)
           Console.WriteLine("Value of (a + b) * (c / d) is  : {0}", e);

           e = a + (b * c) / d;    //  20 + (150/5)
           Console.WriteLine("Value of a + (b * c) / d is  : {0}", e);
           Console.ReadLine();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Value of (a + b) * c / d is : 90
  Value of ((a + b) * c) / d is  : 90
  Value of (a + b) * (c / d) is  : 90
  Value of a + (b * c) / d is  : 50

----------

C# - Decision Making

Decision making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general from of a typical decision making structure found in most of the programming languages:

          |
          v       if condition is false
    < condition >------------>-----------+
          |                              |
          v if condition is true         v
          |                              |
          +-----------------<------------+
          |
  [ conditional code ]
          |
          v

C# provides following types of decision making statements. Click the following links to check their detail.

  +---------------+---------------------------------------------------+
  | Statement     | Description                                       |
  +---------------+---------------------------------------------------+
  | if            | An if statement consists of a boolean expression  |
  |               | followed by one or more statements.               |
  +---------------+---------------------------------------------------+
  | if...else     | An if statement can be followed by an optional    |
  |               | else statement, which executes when the boolean   |
  |               | expression is false.                              |
  +---------------+---------------------------------------------------+
  | nested if     | You can use one if or else if statement inside    |
  |               | another if or else if statement(s).               |
  +---------------+---------------------------------------------------+
  | switch        | A switch statement allows a variable to be tested |
  |               | for equality against a list of values.            |
  +---------------+---------------------------------------------------+
  | nested switch | You can use one switch statement inside another   |
  |               | switch statement(s).                              |
  +---------------+---------------------------------------------------+


The ? : Operator:

We have covered conditional operator ? : in previous chapter which can be used to replace if...else statements. It has the following general form:

  Exp1 ? Exp2 : Exp3;

Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.

The value of a ? expression is determined like this: Exp1 is evaluated. If it is true, then Exp2 is evaluated and becomes the value of the entire ? expression. If Exp1 is false, then Exp3 is evaluated and its value becomes the value of the expression.

----------

C# - Loops

There may be a situation, when you need to execute a block of code several number of times. In general statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on.

Programming languages provide various control structures that allow for more complicated execution paths.

A loop statement allows us to execute a statement or group of statements multiple times and following is the general from of a loop statement in most of the programming languages:
Loop Architecture

C# provides following types of loop to handle looping requirements.

  +--------------+----------------------------------------------------+
  | Loop Type    | Description                                        |
  +--------------+----------------------------------------------------+
  | while        | Repeats a statement or group of statements while a |
  |              | given condition is true. It tests the condition    |
  |              | before executing the loop body.                    |
  +--------------+----------------------------------------------------+
  | for          | Executes a sequence of statements multiple times   |
  |              | and abbreviates the code that manages the loop     |
  |              | variable.                                          |
  +--------------+----------------------------------------------------+
  | do...while   | Like a while statement, except that it tests the   |
  |              | condition at the end of the loop body              |
  +--------------+----------------------------------------------------+
  | nested loops | You can use one or more loop inside any another    |
  |              | while, for or do..while loop.                      |
  +--------------+----------------------------------------------------+


Loop Control Statements:

Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed.

C# provides the following control statements. Click the following links to check their details.

  +-------------------+-----------------------------------------------+
  | Control Statement | Description                                   |
  +-------------------+-----------------------------------------------+
  | break             | Terminates the loop or switch statement and   |
  |                   | transfers execution to the statement          |
  |                   | immediately following the loop or switch.     |
  +-------------------+-----------------------------------------------+
  | continue          | Causes the loop to skip the remainder of its  |
  |                   | body and immediately retest its condition     |
  |                   | prior to reiterating.                         |
  +-------------------+-----------------------------------------------+


The Infinite Loop:

A loop becomes infinite loop if a condition never becomes false. The for loop is traditionally used for this purpose. Since none of the three expressions that form the for loop are required, you can make an endless loop by leaving the conditional expression empty.

  using System;

  namespace Loops {
      class Program {
          static void Main(string[] args) {
              for (; ; ) {
                  Console.WriteLine("Hey! I am Trapped");
              }
          }
      }
  }

When the conditional expression is absent, it is assumed to be true. You may have an initialization and increment expression, but programmers more commonly use the for(;;) construct to signify an infinite loop.

----------

C# - Encapsulation

Encapsulation is defined 'as the process of enclosing one or more items within a physical or logical package'. Encapsulation, in object oriented programming methodology, prevents access to implementation details.

Abstraction and encapsulation are related features in object oriented programming. Abstraction allows making relevant information visible and encapsulation enables a programmer to implement the desired level of abstraction.

Encapsulation is implemented by using access specifiers. An access specifier defines the scope and visibility of a class member. C# supports the following access specifiers:

  - Public
  - Private
  - Protected
  - Internal
  - Protected internal


Public Access Specifier

Public access specifier allows a class to expose its member variables and member functions to other functions and objects. Any public member can be accessed from outside the class.

The following example illustrates this:

  using System;

  namespace RectangleApplication
  {
      class Rectangle
      {
          //member variables
          public double length;
          public double width;

          public double GetArea()
          {
              return length * width;
          }
          public void Display()
          {
              Console.WriteLine("Length: {0}", length);
              Console.WriteLine("Width: {0}", width);
              Console.WriteLine("Area: {0}", GetArea());
          }
      }//end class Rectangle
      class ExecuteRectangle
      {
          static void Main(string[] args)
          {
              Rectangle r = new Rectangle();
              r.length = 4.5;
              r.width = 3.5;
              r.Display();
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Length: 4.5
  Width: 3.5
  Area: 15.75

In the preceding example, the member variables length and width are declared public, so they can be accessed from the function Main() using an instance of the Rectangle class, named r.

The member function Display() and GetArea() can also access these variables directly without using any instance of the class.

The member functions Display() is also declared public, so it can also be accessed from Main() using an instance of the Rectangle class, named r.


Private Access Specifier

Private access specifier allows a class to hide its member variables and member functions from other functions and objects. Only functions of the same class can access its private members. Even an instance of a class cannot access its private members.

The following example illustrates this:

  using System;

  namespace RectangleApplication
  {
      class Rectangle
      {
          //member variables
          private double length;
          private double width;

          public void Acceptdetails()
          {
              Console.WriteLine("Enter Length: ");
              length = Convert.ToDouble(Console.ReadLine());
              Console.WriteLine("Enter Width: ");
              width = Convert.ToDouble(Console.ReadLine());
          }
          public double GetArea()
          {
              return length * width;
          }
          public void Display()
          {
              Console.WriteLine("Length: {0}", length);
              Console.WriteLine("Width: {0}", width);
              Console.WriteLine("Area: {0}", GetArea());
          }
      }//end class Rectangle
      class ExecuteRectangle
      {
          static void Main(string[] args)
          {
              Rectangle r = new Rectangle();
              r.Acceptdetails();
              r.Display();
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Enter Length:
  4.4
  Enter Width:
  3.3
  Length: 4.4
  Width: 3.3
  Area: 14.52

In the preceding example, the member variables length and width are declared private, so they cannot be accessed from the function Main(). The member functions AcceptDetails() and Display() can access these variables. Since the member functions AcceptDetails() and Display() are declared public, they can be accessed from Main() using an instance of the Rectangle class, named r.


Protected Access Specifier

Protected access specifier allows a child class to access the member variables and member functions of its base class. This way it helps in implementing inheritance. We will discuss this in more details in the inheritance chapter.
Internal Access Specifier

Internal access specifier allows a class to expose its member variables and member functions to other functions and objects in the current assembly. In other words, any member with internal access specifier can be accessed from any class or method defined within the application in which the member is defined.

The following program illustrates this:

  using System;

  namespace RectangleApplication
  {
      class Rectangle
      {
          //member variables
          internal double length;
          internal double width;

          double GetArea()
          {
              return length * width;
          }
         public void Display()
          {
              Console.WriteLine("Length: {0}", length);
              Console.WriteLine("Width: {0}", width);
              Console.WriteLine("Area: {0}", GetArea());
          }
      }//end class Rectangle
      class ExecuteRectangle
      {
          static void Main(string[] args)
          {
              Rectangle r = new Rectangle();
              r.length = 4.5;
              r.width = 3.5;
              r.Display();
              Console.ReadLine();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Length: 4.5
  Width: 3.5
  Area: 15.75

In the preceding example, notice that the member function GetArea() is not declared with any access specifier. Then what would be the default access specifier of a class member if we don't mention any? It is private.


Protected Internal Access Specifier

The protected internal access specifier allows a class to hide its member variables and member functions from other class objects and functions, except a child class within the same application. This is also used while implementing inheritance.

----------

C# - Methods

A method is a group of statements that together perform a task. Every C# program has at least one class with a method named Main.

To use a method, you need to:

  - Define the method
  - Call the method


Defining Methods in C#

When you define a method, you basically declare the elements of its structure. The syntax for defining a method in C# is as follows:

  <Access Specifier> <Return Type> <Method Name>(Parameter List)
  {
     Method Body
  }

Following are the various elements of a method:

  - Access Specifier: This determines the visibility of a variable or a method from another class.

  - Return type: A method may return a value. The return type is the data type of the value the method returns. If the method is not returning any values, then the return type is void.

  - Method name: Method name is a unique identifier and it is case sensitive. It cannot be same as any other identifier declared in the class.

  - Parameter list: Enclosed between parentheses, the parameters are used to pass and receive data from a method. The parameter list refers to the type, order, and number of the parameters of a method. Parameters are optional; that is, a method may contain no parameters.

  - Method body: This contains the set of instructions needed to complete the required activity.

Example:

Following code snippet shows a function FindMax that takes two integer values and returns the larger of the two. It has public access specifier, so it can be accessed from outside the class using an instance of the class.

  class NumberManipulator
  {
     public int FindMax(int num1, int num2)
     {
        /* local variable declaration */
        int result;

        if (num1 > num2)
           result = num1;
        else
           result = num2;

        return result;
     }
     ...
  }


Calling Methods in C#

You can call a method using the name of the method. The following example illustrates this:

  using System;

  namespace CalculatorApplication
  {
     class NumberManipulator
     {
        public int FindMax(int num1, int num2)
        {
           /* local variable declaration */
           int result;

           if (num1 > num2)
              result = num1;
           else
              result = num2;

           return result;
        }
        static void Main(string[] args)
        {
           /* local variable definition */
           int a = 100;
           int b = 200;
           int ret;
           NumberManipulator n = new NumberManipulator();

           //calling the FindMax method
           ret = n.FindMax(a, b);
           Console.WriteLine("Max value is : {0}", ret );
           Console.ReadLine();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

Max value is : 200

You can also call public method from other classes by using the instance of the class. For example, the method FindMax belongs to the NumberManipulator class, you can call it from another class Test.

  using System;

  namespace CalculatorApplication
  {
      class NumberManipulator
      {
          public int FindMax(int num1, int num2)
          {
              /* local variable declaration */
              int result;

              if (num1 > num2)
                  result = num1;
              else
                  result = num2;

              return result;
          }
      }
      class Test
      {
          static void Main(string[] args)
          {
              /* local variable definition */
              int a = 100;
              int b = 200;
              int ret;
              NumberManipulator n = new NumberManipulator();
              //calling the FindMax method
              ret = n.FindMax(a, b);
              Console.WriteLine("Max value is : {0}", ret );
              Console.ReadLine();

          }
      }
  }

When the above code is compiled and executed, it produces the following result:

Max value is : 200


Recursive Method Call

A method can call itself. This is known as recursion. Following is an example that calculates factorial for a given number using a recursive function:

  using System;

  namespace CalculatorApplication
  {
      class NumberManipulator
      {
          public int factorial(int num)
          {
              /* local variable declaration */
              int result;

              if (num == 1)
              {
                  return 1;
              }
              else
              {
                  result = factorial(num - 1) * num;
                  return result;
              }
          }

          static void Main(string[] args)
          {
              NumberManipulator n = new NumberManipulator();
              //calling the factorial method
              Console.WriteLine("Factorial of 6 is : {0}", n.factorial(6));
              Console.WriteLine("Factorial of 7 is : {0}", n.factorial(7));
              Console.WriteLine("Factorial of 8 is : {0}", n.factorial(8));
              Console.ReadLine();

          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Factorial of 6 is: 720
  Factorial of 7 is: 5040
  Factorial of 8 is: 40320


Passing Parameters to a Method

When method with parameters is called, you need to pass the parameters to the method. In C#, there are three ways that parameters can be passed to a method:

  +----------------------+---------------------------------------------+
  | Mechanism            | Description                                 |
  +----------------------+---------------------------------------------+
  | Value parameters     | This method copies the actual value of an   |
  |                      | argument into the formal parameter of the   |
  |                      | function. In this case, changes made to the |
  |                      | parameter inside the function have no       |
  |                      | effect on the argument.                     |
  +----------------------+---------------------------------------------+
  | Reference parameters | This method copies the reference to the     |
  |                      | memory location of an argument into the     |
  |                      | formal parameter. This means that changes   |
  |                      | made to the parameter affect the argument.  |
  +----------------------+---------------------------------------------+
  | Output parameters    | This method helps in returning more than    |
  |                      | one value.                                  |
  +----------------------+---------------------------------------------+

----------

C# - Nullables

C# provides a special data types, the nullable types, to which you can assign normal range of values as well as null values.

For example, you can store any value from -2,147,483,648 to 2,147,483,647 or null in a Nullable< Int32 > variable. Similarly, you can assign true, false or null in a Nullable< bool > variable. Syntax for declaring a nullable type is as follows:

< data_type> ? <variable_name> = null;

The following example demonstrates use of nullable data types:

  using System;
  namespace CalculatorApplication
  {
     class NullablesAtShow
     {
        static void Main(string[] args)
        {
           int? num1 = null;
           int? num2 = 45;
           double? num3 = new double?();
           double? num4 = 3.14157;

           bool? boolval = new bool?();

           // display the values

           Console.WriteLine("Nullables at Show: {0}, {1}, {2}, {3}",
                              num1, num2, num3, num4);
           Console.WriteLine("A Nullable boolean value: {0}", boolval);
           Console.ReadLine();

        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Nullables at Show: , 45,  , 3.14157
  A Nullable boolean value:


The Null Coalescing Operator (??)

The null coalescing operator is used with the nullable value types and reference types. It is used for converting an operand to the type of another nullable (or not) value type operand, where an implicit conversion is possible.

If the value of the first operand is null, then the operator returns the value of the second operand, otherwise it returns the value of the first operand. The following example explains this:

  using System;
  namespace CalculatorApplication
  {
     class NullablesAtShow
     {

        static void Main(string[] args)
        {

           double? num1 = null;
           double? num2 = 3.14157;
           double num3;
           num3 = num1 ?? 5.34;
           Console.WriteLine(" Value of num3: {0}", num3);
           num3 = num2 ?? 5.34;
           Console.WriteLine(" Value of num3: {0}", num3);
           Console.ReadLine();

        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Value of num3: 5.34
  Value of num3: 3.14157

----------

C# - Arrays

An array stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

Instead of declaring individual variables, such as number0, number1, ..., and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and ..., numbers[99] to represent individual variables. A specific element in an array is accessed by an index.

All arrays consist of contiguous memory locations. The lowest address corresponds to the first element and the highest address to the last element.


Arrays in C#

Declaring Arrays

To declare an array in C#, you can use the following syntax:

  datatype[] arrayName;

where,

    datatype   is used to specify the type of elements to be stored in the array.
    [ ]        specifies the rank of the array. The rank specifies the size of the array.
    arrayName  specifies the name of the array.

For example,

  double[] balance;


Initializing an Array

Declaring an array does not initialize the array in the memory. When the array variable is initialized, you can assign values to the array.

Array is a reference type, so you need to use the new keyword to create an instance of the array.

For example,

  double[] balance = new double[10];


Assigning Values to an Array

You can assign values to individual array elements, by using the index number, like:

  double[] balance = new double[10];
  balance[0] = 4500.0;

You can assign values to the array at the time of declaration, like:

  double[] balance = { 2340.0, 4523.69, 3421.0};

You can also create and initialize an array, like:

  int [] marks = new int[5]  { 99,  98, 92, 97, 95};

In the preceding case, you may also omit the size of the array, like:

  int [] marks = new int[]  { 99,  98, 92, 97, 95};

You can also copy an array variable into another target array variable. In that case, both the target and source would point to the same memory location:

  int [] marks = new int[]  { 99,  98, 92, 97, 95};
  int[] score = marks;

When you create an array, C# compiler implicitly initializes each array element to a default value depending on the array type. For example for an int array all elements would be initialized to 0.


Accessing Array Elements

An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array. For example:

  double salary = balance[9];

Following is an example, which will use all the above-mentioned three concepts viz. declaration, assignment and accessing arrays:

  using System;
  namespace ArrayApplication
  {
     class MyArray
     {
        static void Main(string[] args)
        {
           int []  n = new int[10]; /* n is an array of 10 integers */
           int i,j;


           /* initialize elements of array n */
           for ( i = 0; i < 10; i++ )
           {
              n[ i ] = i + 100;
           }

           /* output each array element's value */
           for (j = 0; j < 10; j++ )
           {
              Console.WriteLine("Element[{0}] = {1}", j, n[j]);
           }
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Element[0] = 100
  Element[1] = 101
  Element[2] = 102
  Element[3] = 103
  Element[4] = 104
  Element[5] = 105
  Element[6] = 106
  Element[7] = 107
  Element[8] = 108
  Element[9] = 109


Using the foreach Loop

In the previous example, we have used a for loop for accessing each array element. You can also use a foreach statement to iterate through an array.

  using System;

  namespace ArrayApplication
  {
     class MyArray
     {
        static void Main(string[] args)
        {
           int []  n = new int[10]; /* n is an array of 10 integers */


           /* initialize elements of array n */
           for ( int i = 0; i < 10; i++ )
           {
              n[i] = i + 100;
           }

           /* output each array element's value */
           foreach (int j in n )
           {
              int i = j-100;
              Console.WriteLine("Element[{0}] = {1}", i, j);
              i++;
           }
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Element[0] = 100
  Element[1] = 101
  Element[2] = 102
  Element[3] = 103
  Element[4] = 104
  Element[5] = 105
  Element[6] = 106
  Element[7] = 107
  Element[8] = 108
  Element[9] = 109


C# Arrays in Detail

Arrays are important to C# and should need lots of more detail. There are following few important concepts related to array which should be clear to a C# programmer:

  +-----------------------------+--------------------------------------+
  | Arrays concept              | Description                          |
  +-----------------------------+--------------------------------------+
  | Multi-dimensional           | C# supports multidimensional arrays. |
  |                             | The simplest form of the             |
  |                             | multidimensional array is the        |
  |                             | two-dimensional array.               |
  +-----------------------------+--------------------------------------+
  | Jagged                      | C# supports multidimensional arrays, |
  |                             | which are arrays of arrays.          |
  +-----------------------------+--------------------------------------+
  | Passing arrays to functions | You can pass to the function a       |
  |                             | pointer to an array by specifying    |
  |                             | the array's name without an index.   |
  +-----------------------------+--------------------------------------+
  | Param arrays                | This is used for passing unknown     |
  |                             | number of parameters to a function.  |
  +-----------------------------+--------------------------------------+
  | The Array Class             | Defined in System namespace, it is   |
  |                             | the base class to all arrays, and    |
  |                             | provides various properties and      |
  |                             | methods for working with arrays.     |
  +-----------------------------+--------------------------------------+


C# - Multidimensional Arrays

C# allows multidimensional arrays. Multi-dimensional arrays are also called rectangular array.

You can declare a 2-dimensional array of strings as:

  string [,] names;

or, a 3-dimensional array of int variables:

  int [ , , ] m;

Two-Dimensional Arrays:

The simplest form of the multidimensional array is the 2-dimensional array. A 2-dimensional array is, in essence, a list of one-dimensional arrays.

A 2-dimensional array can be thought of as a table, which will have x number of rows and y number of columns. Following is a 2-dimentional array, which contains 3 rows and 4 columns:


Two Dimensional Arrays in C#

Thus, every element in array a is identified by an element name of the form a[ i , j ], where a is the name of the array, and i and j are the subscripts that uniquely identify each element in a.

Initializing Two-Dimensional Arrays

Multidimensional arrays may be initialized by specifying bracketed values for each row. Following is an array with 3 rows and each row has 4 columns.

  int [,] a = int [3,4] = {
      {0, 1, 2, 3} ,   /*  initializers for row indexed by 0 */
      {4, 5, 6, 7} ,   /*  initializers for row indexed by 1 */
      {8, 9, 10, 11}   /*  initializers for row indexed by 2 */
  };


Accessing Two-Dimensional Array Elements

An element in 2-dimensional array is accessed by using the subscripts, i.e., row index and column index of the array. For example:

  int val = a[2,3];

The above statement will take 4th element from the 3rd row of the array. You can verify it in the above diagram. Let us check below program where we have used nested loop to handle a two dimensional array:

  using System;

  namespace ArrayApplication
  {
      class MyArray
      {
          static void Main(string[] args)
          {
              /* an array with 5 rows and 2 columns*/
              int[,] a = new int[5, 2] {{0,0}, {1,2}, {2,4}, {3,6}, {4,8} };

              int i, j;

              /* output each array element's value */
              for (i = 0; i < 5; i++)
              {
                  for (j = 0; j < 2; j++)
                  {
                      Console.WriteLine("a[{0},{1}] = {2}", i, j, a[i,j]);
                  }
              }
             Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  a[0,0]: 0
  a[0,1]: 0
  a[1,0]: 1
  a[1,1]: 2
  a[2,0]: 2
  a[2,1]: 4
  a[3,0]: 3
  a[3,1]: 6
  a[4,0]: 4
  a[4,1]: 8

----------

C# - Jagged Arrays

A Jagged array is an array of arrays. You can declare a jagged array scores of int values as:

  int [][] scores;

Declaring an array, does not create the array in memory. To create the above array:

  int[][] scores = new int[5][];
  for (int i = 0; i < scores.Length; x++)
  {
     scores[i] = new int[4];
  }

You can initialize a jagged array as:

  int[][] scores = new int[2][]{new int[]{92,93,94},new int[]{85,66,87,88}};

Where, scores is an array of two arrays of integers -- scores[0] is an array of 3 integers and scores[1] is an array of 4 integers.
Example

The following example illustrates using a jagged array:

  using System;

  namespace ArrayApplication
  {
      class MyArray
      {
          static void Main(string[] args)
          {
              /* a jagged array of 5 array of integers*/
              int[][] a = new int[][]{new int[]{0,0},new int[]{1,2},
              new int[]{2,4},new int[]{ 3, 6 }, new int[]{ 4, 8 } };

              int i, j;

              /* output each array element's value */
              for (i = 0; i < 5; i++)
              {
                  for (j = 0; j <; 2; j++)
                  {
                      Console.WriteLine("a[{0}][{1}] = {2}", i, j, a[i][j]);
                  }
              }
             Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  a[0][0]: 0
  a[0][1]: 0
  a[1][0]: 1
  a[1][1]: 2
  a[2][0]: 2
  a[2][1]: 4
  a[3][0]: 3
  a[3][1]: 6
  a[4][0]: 4
  a[4][1]: 8

----------

C# - Passing Arrays as Function Arguments

You can pass an array as a function argument in C#. The following example demonstrates this:

  using System;

  namespace ArrayApplication
  {
     class MyArray
     {
        double getAverage(int[] arr, int size)
        {
           int i;
           double avg;
           int sum = 0;

           for (i = 0; i < size; ++i)
           {
              sum += arr[i];
           }

           avg = (double)sum / size;
           return avg;
        }
        static void Main(string[] args)
        {
           MyArray app = new MyArray();
           /* an int array with 5 elements */
           int [] balance = new int[]{1000, 2, 3, 17, 50};
           double avg;

           /* pass pointer to the array as an argument */
           avg = app.getAverage(balance, 5 ) ;

           /* output the returned value */
           Console.WriteLine( "Average value is: {0} ", avg );
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Average value is: 214.4

----------

At times, while declaring a method, you are not sure of the number of arguments passed as a parameter. C# param arrays (or parameter arrays) come into help at these times.

The following example demonstrates this:

  using System;

  namespace ArrayApplication
  {
     class ParamArray
     {
        public int AddElements(params int[] arr)
        {
           int sum = 0;
           foreach (int i in arr)
           {
              sum += i;
           }
           return sum;
        }
     }

     class TestClass
     {
        static void Main(string[] args)
        {
           ParamArray app = new ParamArray();
           int sum = app.AddElements(512, 720, 250, 567, 889);
           Console.WriteLine("The sum is: {0}", sum);
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  The sum is: 2938

----------

C# - Param Arrays

At times, while declaring a method, you are not sure of the number of arguments passed as a parameter. C# param arrays (or parameter arrays) come into help at these times.

The following example demonstrates this:

  using System;

  namespace ArrayApplication
  {
     class ParamArray
     {
        public int AddElements(params int[] arr)
        {
           int sum = 0;
           foreach (int i in arr)
           {
              sum += i;
           }
           return sum;
        }
     }

     class TestClass
     {
        static void Main(string[] args)
        {
           ParamArray app = new ParamArray();
           int sum = app.AddElements(512, 720, 250, 567, 889);
           Console.WriteLine("The sum is: {0}", sum);
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  The sum is: 2938

----------

C# - Array Class

The Array class is the base class for all the arrays in C#. It is defined in the System namespace. The Array class provides various properties and methods to work with arrays.
Properties of the Array Class

The following table provides some of the most commonly used properties of the Array class:

  +-----+---------------+----------------------------------------------+
  | S.N | Property Name | Description                                  |
  +-----+---------------+----------------------------------------------+
  | 1   | IsFixedSize   | Gets a value indicating whether the Array    |
  |     |               | has a fixed size.                            |
  +-----+---------------+----------------------------------------------+
  | 2   | IsReadOnly    | Gets a value indicating whether the Array is |
  |     |               | read-only.                                   |
  +-----+---------------+----------------------------------------------+
  | 3   | Length        | Gets a 32-bit integer that represents the    |
  |     |               | total number of elements in all the          |
  |     |               | dimensions of the Array.                     |
  +-----+---------------+----------------------------------------------+
  | 4   | LongLength    | Gets a 64-bit integer that represents the    |
  |     |               | total number of elements in all the          |
  |     |               | dimensions of the Array.                     |
  +-----+---------------+----------------------------------------------+
  | 5   | Rank          | Gets the rank (number of dimensions) of the  |
  |     |               | Array.                                       |
  +-----+---------------+----------------------------------------------+


Methods of the Array Class

The following table provides some of the most commonly used properties of the Array class:

  +-----+---------------------------+----------------------------------+
  | S.N | Method Name               | Description                      |
  +-----+---------------------------+----------------------------------+
  | 1   | Clear                     | Sets a range of elements in the  |
  |     |                           | Array to zero, to false, or to   |
  |     |                           | null, depending on the element   |
  |     |                           | type.                            |
  +-----+---------------------------+----------------------------------+
  | 2   | Copy(Array, Array, Int32) | Copies a range of elements from  |
  |     |                           | an Array starting at the first   |
  |     |                           | element and pastes them into     |
  |     |                           | another Array starting at the    |
  |     |                           | first element. The length is     |
  |     |                           | specified as a 32-bit integer.   |
  +-----+---------------------------+----------------------------------+
  | 3   | CopyTo(Array, Int32)      | Copies all the elements of the   |
  |     |                           | current one-dimensional Array to |
  |     |                           | the specified one-dimensional    |
  |     |                           | Array starting at the specified  |
  |     |                           | destination Array index. The     |
  |     |                           | index is specified as a 32-bit   |
  |     |                           | integer.                         |
  +-----+---------------------------+----------------------------------+
  | 4   | GetLength                 | Gets a 32-bit integer that       |
  |     |                           | represents the number of elements|
  |     |                           | in the specified dimension of the|
  |     |                           | Array.                           |
  +-----+---------------------------+----------------------------------+
  | 5   | GetLongLength             | Gets a 64-bit integer that       |
  |     |                           | represents the number of elements|
  |     |                           | in the specified dimension of the|
  |     |                           | Array.                           |
  +-----+---------------------------+----------------------------------+
  | 6   | GetLowerBound             | Gets the lower bound of the      |
  |     |                           | specified dimension in the Array.|
  +-----+---------------------------+----------------------------------+
  | 7   | GetType                   | Gets the Type of the current     |
  |     |                           | instance. (Inherited from        |
  |     |                           | Object.)                         |
  +-----+---------------------------+----------------------------------+
  | 8   | GetUpperBound             | Gets the upper bound of the      |
  |     |                           | specified dimension in the Array.|
  +-----+---------------------------+----------------------------------+
  | 9   | GetValue(Int32)           | Gets the value at the specified  |
  |     |                           | position in the one-dimensional  |
  |     |                           | Array. The index is specified as |
  |     |                           | a 32-bit integer.                |
  +-----+---------------------------+----------------------------------+
  | 10  | IndexOf(Array, Object)    | Searches for the specified object|
  |     |                           | and returns the index of the     |
  |     |                           | first occurrence within the      |
  |     |                           | entire one-dimensional Array.    |
  +-----+---------------------------+----------------------------------+
  | 11  | Reverse(Array)            | Reverses the sequence of the     |
  |     |                           | elements in the entire           |
  |     |                           | one-dimensional Array.           |
  +-----+---------------------------+----------------------------------+
  | 12  | SetValue(Object, Int32)   | Sets a value to the element at   |
  |     |                           | the specified position in the    |
  |     |                           | one-dimensional Array. The index |
  |     |                           | is specified as a 32-bit integer.|
  +-----+---------------------------+----------------------------------+
  | 13  | Sort(Array)               | Sorts the elements in an entire  |
  |     |                           | one-dimensional Array using the  |
  |     |                           | IComparable implementation of    |
  |     |                           | each element of the Array.       |
  +-----+---------------------------+----------------------------------+
  | 14  | ToStringk                 | Returns a string that represents |
  |     |                           | the current object. (Inherited   |
  |     |                           | from Object.)                    |
  +-----+---------------------------+----------------------------------+


For complete list of Array class properties and methods, please consult Microsoft documentation on C#.

Example

The following program demonstrates use of some of the methods of the Array class:

  using System;
  namespace ArrayApplication
  {
      class MyArray
      {

          static void Main(string[] args)
          {
              int[] list = { 34, 72, 13, 44, 25, 30, 10 };
              int[] temp = list;

              Console.Write("Original Array: ");
              foreach (int i in list)
              {
                  Console.Write(i + " ");
              }
              Console.WriteLine();

              // reverse the array
              Array.Reverse(temp);
              Console.Write("Reversed Array: ");
              foreach (int i in temp)
              {
                  Console.Write(i + " ");
              }
              Console.WriteLine();

              //sort the array
              Array.Sort(list);
              Console.Write("Sorted Array: ");
              foreach (int i in list)
              {
                  Console.Write(i + " ");
              }
              Console.WriteLine();

             Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Original Array: 34 72 13 44 25 30 10
  Reversed Array: 10 30 25 44 13 72 34
  Sorted Array: 10 13 25 30 34 44 72

----------

C# - Strings

In C#, you can use strings as array of characters, however, more common practice is to use the string keyword to declare a string variable. The string keyword is an alias for the System.String class.


Creating a String Object

You can create string object using one of the following methods:

  - By assigning a string literal to a String variable
  - By using a String class constructor
  - By using the string concatenation operator (+)
  - By retrieving a property or calling a method that returns a string
  - By calling a formatting method to convert a value or object to its string representation

The following example demonstrates this:

  using System;

  namespace StringApplication
  {
      class Program
      {
          static void Main(string[] args)
          {
             //from string literal and string concatenation
              string fname, lname;
              fname = "Rowan";
              lname = "Atkinson";

              string fullname = fname + lname;
              Console.WriteLine("Full Name: {0}", fullname);

              //by using string constructor
              char[] letters = { 'H', 'e', 'l', 'l','o' };
              string greetings = new string(letters);
              Console.WriteLine("Greetings: {0}", greetings);

              //methods returning string
              string[] sarray = { "Hello", "From", "Tutorials", "Point" };
              string message = String.Join(" ", sarray);
              Console.WriteLine("Message: {0}", message);

              //formatting method to convert a value
              DateTime waiting = new DateTime(2012, 10, 10, 17, 58, 1);
              string chat = String.Format("Message sent at {0:t} on {0:D}",
              waiting);
              Console.WriteLine("Message: {0}", chat);
              Console.ReadKey() ;
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Full Name: Rowan Atkinson
  Greetings: Hello
  Message: Hello From Tutorials Point
  Message: Message sent at 5:58 PM on Wednesday, October 10, 2012


Properties of the String Class

The String class has the following two properties:

  +-----+---------------+----------------------------------------------+
  | S.N | Property Name | Description                                  |
  +-----+---------------+----------------------------------------------+
  | 1   | Chars         | Gets the Char object at a specified position |
  |     |               | in the current String object.                |
  +-----+---------------+----------------------------------------------+
  | 2   | Length        | Gets the number of characters in the current |
  |     |               | String object.                               |
  +-----+---------------+----------------------------------------------+


Methods of the String Class

The String class has numerous methods that help you in working with the string objects. The following table provides some of the most commonly used methods:

  +-----+--------------------------------------------------------------+
  | S.N | Method Name & Description                                    |
  +-----+--------------------------------------------------------------+
  | 1   | public static int Compare( string strA, string strB )        |
  |     |                                                              |
  |     | Compares two specified string objects and returns an integer |
  |     | that indicates their relative position in the sort order.    |
  +-----+---------------+----------------------------------------------+
  | 2   | public static int Compare(                                   |
  |     |     string strA,                                             |
  |     |     string strB,                                             |
  |     |     bool ignoreCase                                          |
  |     | )                                                            |
  |     |                                                              |
  |     | Compares two specified string objects and returns an integer |
  |     | that indicates their relative position in the sort order.    |
  |     | However, it ignores case if the Boolean parameter is true.   |
  +-----+---------------+----------------------------------------------+
  | 3   | public static string Concat( string str0, string str1 )      |
  |     |                                                              |
  |     | Concatenates two string objects.                             |
  +-----+---------------+----------------------------------------------+
  | 4   | public static string Concat(                                 |
  |     |     string str0,                                             |
  |     |     string str1,                                             |
  |     |     string str2                                              |
  |     | )                                                            |
  |     |                                                              |
  |     | Concatenates three string objects.                           |
  +-----+--------------------------------------------------------------+
  | 5   | public static string Concat(                                 |
  |     |     string str0,                                             |
  |     |     string str1,                                             |
  |     |     string str2,                                             |
  |     |     string str3                                              |
  |     | )                                                            |
  |     | Concatenates four string objects.                            |
  +-----+--------------------------------------------------------------+
  | 6   | public bool Contains( string value )                         |
  |     |                                                              |
  |     | Returns a value indicating whether the specified string      |
  |     | object occurs within this string.                            |
  +-----+--------------------------------------------------------------+
  | 7   | public static string Copy( string str )                      |
  |     | Creates a new String object with the same value as the       |
  |     | specified string.                                            |
  +-----+--------------------------------------------------------------+
  | 8   | public void CopyTo(                                          |
  |     |      int sourceIndex,                                        |
  |     |      char[] destination,                                     |
  |     |      int destinationIndex,                                   |
  |     |      int count                                               |
  |     |  )                                                           |
  |     |                                                              |
  |     | Copies a specified number of characters from a specified     |
  |     | position of the string object to a specified position in an  |
  |     | array of Unicode characters.                                 |
  +-----+--------------------------------------------------------------+
  | 9   | public bool EndsWith( string value )                         |
  |     |                                                              |
  |     | Determines whether the end of the string object matches the  |
  |     | specified string.                                            |
  +-----+--------------------------------------------------------------+
  | 10  | public bool Equals( string value )                           |
  |     |                                                              |
  |     | Determines whether the current string object and the         |
  |     | specified string object have the same value.                 |
  +-----+--------------------------------------------------------------+
  | 11  | public static bool Equals( string a, string b )              |
  |     |                                                              |
  |     | Determines whether two specified string objects have the     |
  |     | same value.                                                  |
  +-----+--------------------------------------------------------------+
  | 12  | public static string Format( string format, Object arg0 )    |
  |     |                                                              |
  |     | Replaces one or more format items in a specified string with |
  |     | the string representation of a specified object.             |
  +-----+--------------------------------------------------------------+
  | 13  | public int IndexOf( char value )                             |
  |     |                                                              |
  |     | Returns the zero-based index of the first occurrence of the  |
  |     | specified Unicode character in the current string.           |
  +-----+--------------------------------------------------------------+
  | 14  | public int IndexOf( string value )                           |
  |     |                                                              |
  |     | Returns the zero-based index of the first occurrence of the  |
  |     | specified string in this instance.                           |
  +-----+--------------------------------------------------------------+
  | 15  | public int IndexOf( char value, int startIndex )             |
  |     |                                                              |
  |     | Returns the zero-based index of the first occurrence of the  |
  |     | specified Unicode character in this string, starting search  |
  |     | at the specified character position.                         |
  +-----+--------------------------------------------------------------+
  | 16  | public int IndexOf( string value, int startIndex )           |
  |     |                                                              |
  |     | Returns the zero-based index of the first occurrence of the  |
  |     | specified string in this instance, starting search at the    |
  |     | specified character position.                                |
  +-----+--------------------------------------------------------------+
  | 17  | public int IndexOfAny( char[] anyOf )                        |
  |     |                                                              |
  |     | Returns the zero-based index of the first occurrence in this |
  |     | instance of any character in a specified array of Unicode    |
  |     | characters.                                                  |
  +-----+--------------------------------------------------------------+
  | 18  | public int IndexOfAny( char[] anyOf, int startIndex )        |
  |     |                                                              |
  |     | Returns the zero-based index of the first occurrence in this |
  |     | instance of any character in a specified array of Unicode    |
  |     | characters, starting search at the specified character       |
  |     | position.                                                    |
  +-----+--------------------------------------------------------------+
  | 19  | public string Insert( int startIndex, string value )         |
  |     |                                                              |
  |     | Returns a new string in which a specified string is inserted |
  |     | at a specified index position in the current string object.  |
  +-----+--------------------------------------------------------------+
  | 20  | public static bool IsNullOrEmpty( string value )             |
  |     |                                                              |
  |     | Indicates whether the specified string is null or an Empty   |
  |     | string.                                                      |
  +-----+--------------------------------------------------------------+
  | 21  | public static string Join(                                   |
  |     |     string separator,                                        |
  |     |     params string[] value                                    |
  |     | )                                                            |
  |     |                                                              |
  |     | Concatenates all the elements of a string array, using the   |
  |     | specified separator between each element.                    |
  +-----+--------------------------------------------------------------+
  | 22  | public static string Join(                                   |
  |     |     string separator,                                        |
  |     |     string[] value,                                          |
  |     |     int startIndex,                                          |
  |     |     int count                                                |
  |     | )                                                            |
  |     |                                                              |
  |     | Concatenates the specified elements of a string array, using |
  |     | the specified separator between each element.                |
  +-----+--------------------------------------------------------------+
  | 23  | public int LastIndexOf( char value )                         |
  |     |                                                              |
  |     | Returns the zero-based index position of the last occurrence |
  |     | of the specified Unicode character within the current string |
  |     | object.                                                      |
  +-----+--------------------------------------------------------------+
  | 24  | public int LastIndexOf( string value )                       |
  |     |                                                              |
  |     | Returns the zero-based index position of the last occurrence |
  |     | of a specified string within the current string object.      |
  +-----+--------------------------------------------------------------+
  | 25  | public string Remove( int startIndex )                       |
  |     |                                                              |
  |     | Removes all the characters in the current instance, beginning| 
  |     | at a specified position and continuing through the last      |
  |     | position, and returns the string.                            |
  +-----+--------------------------------------------------------------+
  | 26  | public string Remove( int startIndex, int count )            |
  |     |                                                              |
  |     | Removes the specified number of characters in the current    |
  |     | string beginning at a specified position and returns the     |
  |     | string.                                                      |
  +-----+--------------------------------------------------------------+
  | 27  | public string Replace( char oldChar, char newChar )          |
  |     |                                                              |
  |     | Replaces all occurrences of a specified Unicode character in |
  |     | the current string object with the specified Unicode         |
  |     | character and returns the new string.                        |
  +-----+--------------------------------------------------------------+
  | 28  | public string Replace( string oldValue, string newValue )    |
  |     |                                                              |
  |     | Replaces all occurrences of a specified string in the current| 
  |     | string object with the specified string and returns the new  |
  |     | string.                                                      |
  +-----+--------------------------------------------------------------+
  | 29  | public string[] Split( params char[] separator )             |
  |     |                                                              |
  |     | Returns a string array that contains the substrings in the   |
  |     | current string object, delimited by elements of a specified  |
  |     | Unicode character array.                                     |
  +-----+--------------------------------------------------------------+
  | 30  | public string[] Split( char[] separator, int count )         |
  |     |                                                              |
  |     | Returns a string array that contains the substrings in the   |
  |     | current string object, delimited by elements of a specified  |
  |     | Unicode character array. The int parameter specifies the     |
  |     | maximum number of substrings to return.                      |
  +-----+--------------------------------------------------------------+
  | 31  | public bool StartsWith( string value )                       |
  |     |                                                              |
  |     | Determines whether the beginning of this string instance     |
  |     | matches the specified string.                                |
  +-----+--------------------------------------------------------------+
  | 32  | public char[] ToCharArray()                                  |
  |     |                                                              |
  |     | Returns a Unicode character array with all the characters in |
  |     | the current string object.                                   |
  +-----+--------------------------------------------------------------+
  | 33  | public char[] ToCharArray( int startIndex, int length )      |
  |     |                                                              |
  |     | Returns a Unicode character array with all the characters in |
  |     | the current string object, starting from the specified index |
  |     | and up to the specified length.                              |
  +-----+--------------------------------------------------------------+
  | 34  | public string ToLower()                                      |
  |     |                                                              |
  |     | Returns a copy of this string converted to lowercase.        |
  +-----+--------------------------------------------------------------+
  | 35  | public string ToUpper()                                      |
  |     |                                                              |
  |     | Returns a copy of this string converted to uppercase.        |
  +-----+--------------------------------------------------------------+
  | 36  | public string Trim()                                         |
  |     |                                                              |
  |     | Removes all leading and trailing white-space characters from |
  |     | the current String object.                                   |
  +-----+--------------------------------------------------------------+


The above list of methods is not exhaustive, please visit MSDN library for the complete list of methods and String class constructors.

Examples:

The following example demonstrates some of the methods mentioned above:

Comparing Strings:

  using System;

  namespace StringApplication
  {
     class StringProg
     {
        static void Main(string[] args)
        {
           string str1 = "This is test";
           string str2 = "This is text";

           if (String.Compare(str1, str2) == 0)
           {
              Console.WriteLine(str1 + " and " + str2 +  " are equal.");
           }
           else
           {
              Console.WriteLine(str1 + " and " + str2 + " are not equal.");
           }
           Console.ReadKey() ;
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

This is test and This is text are not equal.

String Contains String:

  using System;

  namespace StringApplication
  {
     class StringProg
     {
        static void Main(string[] args)
        {
           string str = "This is test";
           if (str.Contains("test"))
           {
              Console.WriteLine("The sequence 'test' was found.");
           }
           Console.ReadKey() ;
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

The sequence 'test' was found.

Getting a Substring:

  using System;

  namespace StringApplication
  {
     class StringProg
     {
        static void Main(string[] args)
        {
           string str = "Last night I dreamt of San Pedro";
           Console.WriteLine(str);
           string substr = str.Substring(23);
           Console.WriteLine(substr);
        }
        Console.ReadKey() ;
     }
  }

When the above code is compiled and executed, it produces the following result:

  San Pedro

Joining Strings:

  using System;

  namespace StringApplication
  {
     class StringProg
     {
        static void Main(string[] args)
        {
           string[] starray = new string[]{"Down the way nights are dark",
           "And the sun shines daily on the mountain top",
           "I took a trip on a sailing ship",
           "And when I reached Jamaica",
           "I made a stop"};

           string str = String.Join("\n", starray);
           Console.WriteLine(str);
        }
        Console.ReadKey() ;
     }
  }

When the above code is compiled and executed, it produces the following result:

  Down the way nights are dark
  And the sun shines daily on the mountain top
  I took a trip on a sailing ship
  And when I reached Jamaica
  I made a stop

----------

C# - Structures

In C#, a structure is a value type data type. It helps you to make a single variable hold related data of various data types. The struct keyword is used for creating a structure.

Structures are used to represent a record. Suppose you want to keep track of your books in a library. You might want to track the following attributes about each book:

  - Title
  - Author
  - Subject
  - Book ID


Defining a Structure

To define a structure, you must use the struct statement. The struct statement defines a new data type, with more than one member for your program.

For example, here is the way you would declare the Book structure:

  struct Books
  {
     public string title;
     public string author;
     public string subject;
     public int book_id;
  };

The following program shows the use of the structure:

  using System;

  struct Books
  {
     public string title;
     public string author;
     public string subject;
     public int book_id;
  };

  public class testStructure
  {
     public static void Main(string[] args)
     {

        Books Book1;        /* Declare Book1 of type Book */
        Books Book2;        /* Declare Book2 of type Book */

        /* book 1 specification */
        Book1.title = "C Programming";
        Book1.author = "Nuha Ali";
        Book1.subject = "C Programming Tutorial";
        Book1.book_id = 6495407;

        /* book 2 specification */
        Book2.title = "Telecom Billing";
        Book2.author = "Zara Ali";
        Book2.subject =  "Telecom Billing Tutorial";
        Book2.book_id = 6495700;

        /* print Book1 info */
        Console.WriteLine( "Book 1 title : {0}", Book1.title);
        Console.WriteLine("Book 1 author : {0}", Book1.author);
        Console.WriteLine("Book 1 subject : {0}", Book1.subject);
        Console.WriteLine("Book 1 book_id :{0}", Book1.book_id);

        /* print Book2 info */
        Console.WriteLine("Book 2 title : {0}", Book2.title);
        Console.WriteLine("Book 2 author : {0}", Book2.author);
        Console.WriteLine("Book 2 subject : {0}", Book2.subject);
        Console.WriteLine("Book 2 book_id : {0}", Book2.book_id);

        Console.ReadKey();
     }
  }

When the above code is compiled and executed, it produces the following result:

  Book 1 title : C Programming
  Book 1 author : Nuha Ali
  Book 1 subject : C Programming Tutorial
  Book 1 book_id : 6495407
  Book 2 title : Telecom Billing
  Book 2 author : Zara Ali
  Book 2 subject : Telecom Billing Tutorial
  Book 2 book_id : 6495700

Features of C# Structures

You have already used a simple structure named Books. Structures in C# are quite different from that in traditional C or C++. The C# structures have the following features:

  - Structures can have methods, fields, indexers, properties, operator methods, and events.
  - Structures can have defined constructors, but not destructors. However, you cannot define a default constructor for a structure. The default constructor is automatically defined and can't be changed.
  - Unlike classes, structures cannot inherit other structures or classes.
  - Structures cannot be used as a base for other structures or classes.
  - A structure can implement one or more interfaces.
  - Structure members cannot be specified as abstract, virtual, or protected.
  - When you create a struct object using the New operator, it gets created and the appropriate constructor is called. Unlike classes, structs can be instantiated without using the New operator.
  - If the New operator is not used, the fields will remain unassigned and the object cannot be used until all the fields are initialized.


Class vs Structure

Classes and Structures have the following basic differences:

  - classes are reference types and structs are value types
  - structures do not support inheritance
  - structures cannot have default constructor

In the light of the above discussions, let us rewrite the previous example:

  using System;

  struct Books
  {
     private string title;
     private string author;
     private string subject;
     private int book_id;
     public void getValues(string t, string a, string s, int id)
     {
        title = t;
        author = a;
        subject = s;
        book_id = id;
     }
     public void display()
     {
        Console.WriteLine("Title : {0}", title);
        Console.WriteLine("Author : {0}", author);
        Console.WriteLine("Subject : {0}", subject);
        Console.WriteLine("Book_id :{0}", book_id);
     }

  };

  public class testStructure
  {
     public static void Main(string[] args)
     {

        Books Book1 = new Books(); /* Declare Book1 of type Book */
        Books Book2 = new Books(); /* Declare Book2 of type Book */

        /* book 1 specification */
        Book1.getValues("C Programming",
        "Nuha Ali", "C Programming Tutorial",6495407);

        /* book 2 specification */
        Book2.getValues("Telecom Billing",
        "Zara Ali", "Telecom Billing Tutorial", 6495700);

        /* print Book1 info */
        Book1.display();

        /* print Book2 info */
        Book2.display();

        Console.ReadKey();

     }
  }

When the above code is compiled and executed, it produces the following result:

  Title : C Programming
  Author : Nuha Ali
  Subject : C Programming Tutorial
  Book_id : 6495407
  Title : Telecom Billing
  Author : Zara Ali
  Subject : Telecom Billing Tutorial
  Book_id : 6495700

----------

C# - Enums

An enumeration is a set of named integer constants. An enumerated type is declared using the enum keyword.

C# enumerations are value data type. In other words, enumeration contains its own values and cannot inherit or cannot pass inheritance.
Declaring enum Variable

The general syntax for declaring an enumeration is:

  enum <enum_name>
  {
      enumeration list
  };

Where,

    The enum_name specifies the enumeration type name.

    The enumeration list is a comma-separated list of identifiers.

Each of the symbols in the enumeration list stands for an integer value, one greater than the symbol that precedes it. By default, the value of the first enumeration symbol is 0. For example:

  enum Days { Sun, Mon, tue, Wed, thu, Fri, Sat };

Example:

The following example demonstrates use of enum variable:

  using System;
  namespace EnumApplication
  {
     class EnumProgram
     {
        enum Days { Sun, Mon, tue, Wed, thu, Fri, Sat };

        static void Main(string[] args)
        {
           int WeekdayStart = (int)Days.Mon;
           int WeekdayEnd = (int)Days.Fri;
           Console.WriteLine("Monday: {0}", WeekdayStart);
           Console.WriteLine("Friday: {0}", WeekdayEnd);
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Monday: 1
  Friday: 5

----------

C# - Classes

When you define a class, you define a blueprint for a data type. This doesn't actually define any data, but it does define what the class name means, that is, what an object of the class will consist of and what operations can be performed on such an object. Objects are instances of a class. The methods and variables that constitute a class are called members of the class.


Class Definition

A class definition starts with the keyword class followed by the class name; and the class body, enclosed by a pair of curly braces. Following is the general form of a class definition:

  <access specifier> class  class_name
  {
      // member variables
      <access specifier> <data type> variable1;
      <access specifier> <data type> variable2;
      ...
      <access specifier> <data type> variableN;
      // member methods
      <access specifier> <return type> method1(parameter_list)
      {
          // method body
      }
      <access specifier> <return type> method2(parameter_list)
      {
          // method body
      }
      ...
      <access specifier> <return type> methodN(parameter_list)
      {
          // method body
      }
  }

Please note that,

  - Access specifiers specify the access rules for the members as well as the class itself, if not mentioned then the default access specifier for a class type is internal. Default access for the members is private.

  - Data type specifies the type of variable, and return type specifies the data type of the data, the method returns, if any.

  - To access the class members, you will use the dot (.) operator.

  - The dot operator links the name of an object with the name of a member.

The following example illustrates the concepts discussed so far:

  using System;
  namespace BoxApplication
  {
      class Box
      {
         public double length;   // Length of a box
         public double breadth;  // Breadth of a box
         public double height;   // Height of a box
      }
      class Boxtester
      {
          static void Main(string[] args)
          {
              Box Box1 = new Box();        // Declare Box1 of type Box
              Box Box2 = new Box();        // Declare Box2 of type Box
              double volume = 0.0;         // Store the volume of a box here

              // box 1 specification
              Box1.height = 5.0;
              Box1.length = 6.0;
              Box1.breadth = 7.0;

              // box 2 specification
              Box2.height = 10.0;
              Box2.length = 12.0;
              Box2.breadth = 13.0;

              // volume of box 1
              volume = Box1.height * Box1.length * Box1.breadth;
              Console.WriteLine("Volume of Box1 : {0}",  volume);

              // volume of box 2
              volume = Box2.height * Box2.length * Box2.breadth;
              Console.WriteLine("Volume of Box2 : {0}", volume);
              Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Volume of Box1 : 210
  Volume of Box2 : 1560

Member Functions and Encapsulation

A member function of a class is a function that has its definition or its prototype within the class definition like any other variable. It operates on any object of the class of which it is a member, and has access to all the members of a class for that object.

Member variables are attributes of an object (from design perspective) and they are kept private to implement encapsulation. These variables can only be accessed using the public member functions.

Let us put above concepts to set and get the value of different class members in a class:

  using System;
  namespace BoxApplication
  {
      class Box
      {
         private double length;   // Length of a box
         private double breadth;  // Breadth of a box
         private double height;   // Height of a box
         public void setLength( double len )
         {
              length = len;
         }

         public void setBreadth( double bre )
         {
              breadth = bre;
         }

         public void setHeight( double hei )
         {
              height = hei;
         }
         public double getVolume()
         {
             return length * breadth * height;
         }
      }
      class Boxtester
      {
          static void Main(string[] args)
          {
              Box Box1 = new Box();        // Declare Box1 of type Box
              Box Box2 = new Box();
              double volume;


              // Declare Box2 of type Box
              // box 1 specification
              Box1.setLength(6.0);
              Box1.setBreadth(7.0);
              Box1.setHeight(5.0);

              // box 2 specification
              Box2.setLength(12.0);
              Box2.setBreadth(13.0);
              Box2.setHeight(10.0);

              // volume of box 1
              volume = Box1.getVolume();
              Console.WriteLine("Volume of Box1 : {0}" ,volume);

              // volume of box 2
              volume = Box2.getVolume();
              Console.WriteLine("Volume of Box2 : {0}", volume);

              Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Volume of Box1 : 210
  Volume of Box2 : 1560


Constructors in C#

A class constructor is a special member function of a class that is executed whenever we create new objects of that class.

A constructor will have exact same name as the class and it does not have any return type. Following example explains the concept of constructor:

  using System;
  namespace LineApplication
  {
     class Line
     {
        private double length;   // Length of a line
        public Line()
        {
           Console.WriteLine("Object is being created");
        }

        public void setLength( double len )
        {
           length = len;
        }
        public double getLength()
        {
           return length;
        }

        static void Main(string[] args)
        {
           Line line = new Line();
           // set line length
           line.setLength(6.0);
           Console.WriteLine("Length of line : {0}", line.getLength());
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Object is being created
  Length of line : 6

A default constructor does not have any parameter but if you need a constructor can have parameters. Such constructors are called parameterized constructors. This technique helps you to assign initial value to an object at the time of its creation as shown in the following example:

  using System;
  namespace LineApplication
  {
     class Line
     {
        private double length;   // Length of a line
        public Line(double len)  //Parameterized constructor
        {
           Console.WriteLine("Object is being created, length = {0}", len);
           length = len;
        }

        public void setLength( double len )
        {
           length = len;
        }
        public double getLength()
        {
           return length;
        }

        static void Main(string[] args)
        {
           Line line = new Line(10.0);
           Console.WriteLine("Length of line : {0}", line.getLength());
           // set line length
           line.setLength(6.0);
           Console.WriteLine("Length of line : {0}", line.getLength());
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Object is being created, length = 10
  Length of line : 10
  Length of line : 6


Destructors in C#

A destructor is a special member function of a class that is executed whenever an object of its class goes out of scope. A destructor will have exact same name as the class prefixed with a tilde (~) and it can neither return a value nor can it take any parameters.

Destructor can be very useful for releasing resources before coming out of the program like closing files, releasing memories etc. Destructors cannot be inherited or overloaded.

Following example explains the concept of destructor:

  using System;
  namespace LineApplication
  {
     class Line
     {
        private double length;   // Length of a line
        public Line()  // constructor
        {
           Console.WriteLine("Object is being created");
        }
        ~Line() //destructor
        {
           Console.WriteLine("Object is being deleted");
        }

        public void setLength( double len )
        {
           length = len;
        }
        public double getLength()
        {
           return length;
        }

        static void Main(string[] args)
        {
           Line line = new Line();
           // set line length
           line.setLength(6.0);
           Console.WriteLine("Length of line : {0}", line.getLength());
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Object is being created
  Length of line : 6
  Object is being deleted


Static Members of a C# Class

We can define class members as static using the static keyword. When we declare a member of a class as static, it means no matter how many objects of the class are created, there is only one copy of the static member.

The keyword static implies that only one instance of the member exists for a class. Static variables are used for defining constants because their values can be retrieved by invoking the class without creating an instance of it. Static variables can be initialized outside the member function or class definition. You can also initialize static variables inside the class definition.

The following example demonstrates the use of static variables:

  using System;
  namespace StaticVarApplication
  {
      class StaticVar
      {
         public static int num;
          public void count()
          {
              num++;
          }
          public int getNum()
          {
              return num;
          }
      }
      class StaticTester
      {
          static void Main(string[] args)
          {
              StaticVar s1 = new StaticVar();
              StaticVar s2 = new StaticVar();
              s1.count();
              s1.count();
              s1.count();
              s2.count();
              s2.count();
              s2.count();
              Console.WriteLine("Variable num for s1: {0}", s1.getNum());
              Console.WriteLine("Variable num for s2: {0}", s2.getNum());
              Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Variable num for s1: 6
  Variable num for s2: 6

You can also declare a member function as static. Such functions can access only static variables. The static functions exist even before the object is created. The following example demonstrates the use of static functions:

  using System;
  namespace StaticVarApplication
  {
      class StaticVar
      {
         public static int num;
          public void count()
          {
              num++;
          }
          public static int getNum()
          {
              return num;
          }
      }
      class StaticTester
      {
          static void Main(string[] args)
          {
              StaticVar s = new StaticVar();
              s.count();
              s.count();
              s.count();
              Console.WriteLine("Variable num: {0}", StaticVar.getNum());
              Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

Variable num: 3

----------

C# - Inheritance

One of the most important concepts in object-oriented programming is that of inheritance. Inheritance allows us to define a class in terms of another class, which makes it easier to create and maintain an application. This also provides an opportunity to reuse the code functionality and fast implementation time.

When creating a class, instead of writing completely new data members and member functions, the programmer can designate that the new class should inherit the members of an existing class. This existing class is called the base class, and the new class is referred to as the derived class.

The idea of inheritance implements the IS-A relationship. For example, mammal IS A animal, dog IS-A mammal hence dog IS-A animal as well and so on.
Base and Derived Classes

A class can be derived from more than one class or interface, which means that it can inherit data and functions from multiple base class or interface.

The syntax used in C# for creating derived classes is as follows:

  <acess-specifier> class <base_class>
  {
   ...
  }
  class <derived_class> : <base_class>
  {
   ...
  }

Consider a base class Shape and its derived class Rectangle:

  using System;
  namespace InheritanceApplication
  {
     class Shape
     {
        public void setWidth(int w)
        {
           width = w;
        }
        public void setHeight(int h)
        {
           height = h;
        }
        protected int width;
        protected int height;
     }

     // Derived class
     class Rectangle: Shape
     {
        public int getArea()
        {
           return (width * height);
        }
     }

     class RectangleTester
     {
        static void Main(string[] args)
        {
           Rectangle Rect = new Rectangle();

           Rect.setWidth(5);
           Rect.setHeight(7);

           // Print the area of the object.
           Console.WriteLine("Total area: {0}",  Rect.getArea());
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Total area: 35


Base Class Initialization

The derived class inherits the base class member variables and member methods. Therefore the super class object should be created before the subclass is created. You can give instructions for superclass initialization in the member initialization list.

The following program demonstrates this:

  using System;
  namespace RectangleApplication
  {
     class Rectangle
     {
        //member variables
        protected double length;
        protected double width;
        public Rectangle(double l, double w)
        {
           length = l;
           width = w;
        }
        public double GetArea()
        {
           return length * width;
        }
        public void Display()
        {
           Console.WriteLine("Length: {0}", length);
           Console.WriteLine("Width: {0}", width);
           Console.WriteLine("Area: {0}", GetArea());
        }
     }//end class Rectangle
     class Tabletop : Rectangle
     {
        private double cost;
        public Tabletop(double l, double w) : base(l, w)
        { }
        public double GetCost()
        {
           double cost;
           cost = GetArea() * 70;
           return cost;
        }
        public void Display()
        {
           base.Display();
           Console.WriteLine("Cost: {0}", GetCost());
        }
     }
     class ExecuteRectangle
     {
        static void Main(string[] args)
        {
           Tabletop t = new Tabletop(4.5, 7.5);
           t.Display();
           Console.ReadLine();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Length: 4.5
  Width: 7.5
  Area: 33.75
  Cost: 2362.5


Multiple Inheritance in C#

C# does not support multiple inheritance. However, you can use interfaces to implement multiple inheritance. The following program demonstrates this:

  using System;
  namespace InheritanceApplication
  {
     class Shape
     {
        public void setWidth(int w)
        {
           width = w;
        }
        public void setHeight(int h)
        {
           height = h;
        }
        protected int width;
        protected int height;
     }

     // Base class PaintCost
     public interface PaintCost
     {
        int getCost(int area);

     }
     // Derived class
     class Rectangle : Shape, PaintCost
     {
        public int getArea()
        {
           return (width * height);
        }
        public int getCost(int area)
        {
           return area * 70;
        }
     }
     class RectangleTester
     {
        static void Main(string[] args)
        {
           Rectangle Rect = new Rectangle();
           int area;
           Rect.setWidth(5);
           Rect.setHeight(7);
           area = Rect.getArea();
           // Print the area of the object.
           Console.WriteLine("Total area: {0}",  Rect.getArea());
           Console.WriteLine("Total paint cost: ${0}" , Rect.getCost(area));
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Total area: 35
  Total paint cost: $2450

----------

C# - Polymorphism

The word polymorphism means having many forms. In object-oriented programming paradigm, polymorphism is often expressed as 'one interface, multiple functions'.

Polymorphism can be static or dynamic. In static polymorphism the response to a function is determined at the compile time. In dynamic polymorphism , it is decided at run-time.


Static Polymorphism

The mechanism of linking a function with an object during compile time is called early binding. It is also called static binding. C# provides two techniques to implement static polymorphism. These are:

  - Function overloading

  - Operator overloading

We will discuss function overloading in the next section and operator overloading will be dealt with in next chapter.
Function Overloading

You can have multiple definitions for the same function name in the same scope. The definition of the function must differ from each other by the types and/or the number of arguments in the argument list. You cannot overload function declarations that differ only by return type.

Following is the example where same function print() is being used to print different data types:

  using System;
  namespace PolymorphismApplication
  {
     class Printdata
     {
        void print(int i)
        {
           Console.WriteLine("Printing int: {0}", i );
        }

        void print(double f)
        {
           Console.WriteLine("Printing float: {0}" , f);
        }

        void print(string s)
        {
           Console.WriteLine("Printing string: {0}", s);
        }
        static void Main(string[] args)
        {
           Printdata p = new Printdata();
           // Call print to print integer
           p.print(5);
           // Call print to print float
           p.print(500.263);
           // Call print to print string
           p.print("Hello C++");
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Printing int: 5
  Printing float: 500.263
  Printing string: Hello C++


Dynamic Polymorphism

C# allows you to create abstract classes that are used to provide partial class implementation of an interface. Implementation is completed when a derived class inherits from it. Abstract classes contain abstract methods, which are implemented by the derived class. The derived classes have more specialized functionality.

Please note the following rules about abstract classes:

  - You cannot create an instance of an abstract class

  - You cannot declare an abstract method outside an abstract class

  - When a class is declared sealed, it cannot be inherited, abstract classes cannot be declared sealed.

The following program demonstrates an abstract class:

  using System;
  namespace PolymorphismApplication
  {
     abstract class Shape
     {
        public abstract int area();
     }
     class Rectangle:  Shape
     {
        private int length;
        private int width;
        public Rectangle( int a=0, int b=0)
        {
           length = a;
           width = b;
        }
        public override int area ()
        {
           Console.WriteLine("Rectangle class area :");
           return (width * length);
        }
     }

     class RectangleTester
     {
        static void Main(string[] args)
        {
           Rectangle r = new Rectangle(10, 7);
           double a = r.area();
           Console.WriteLine("Area: {0}",a);
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Rectangle class area :
  Area: 70

When you have a function defined in a class that you want to be implemented in an inherited class(es), you use virtual functions. The virtual functions could be implemented differently in different inherited class and the call to these functions will be decided at runtime.

Dynamic polymorphism is implemented by abstract classes and virtual functions.

The following program demonstrates this:

  using System;
  namespace PolymorphismApplication
  {
     class Shape
     {
        protected int width, height;
        public Shape( int a=0, int b=0)
        {
           width = a;
           height = b;
        }
        public virtual int area()
        {
           Console.WriteLine("Parent class area :");
           return 0;
        }
     }
     class Rectangle: Shape
     {
        public Rectangle( int a=0, int b=0): base(a, b)
        {

        }
        public override int area ()
        {
           Console.WriteLine("Rectangle class area :");
           return (width * height);
        }
     }
     class Triangle: Shape
     {
        public Triangle(int a = 0, int b = 0): base(a, b)
        {

        }
        public override int area()
        {
           Console.WriteLine("Triangle class area :");
           return (width * height / 2);
        }
     }
     class Caller
     {
        public void CallArea(Shape sh)
        {
           int a;
           a = sh.area();
           Console.WriteLine("Area: {0}", a);
        }
     }
     class Tester
     {

        static void Main(string[] args)
        {
           Caller c = new Caller();
           Rectangle r = new Rectangle(10, 7);
           Triangle t = new Triangle(10, 5);
           c.CallArea(r);
           c.CallArea(t);
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Rectangle class area:
  Area: 70
  Triangle class area:
  Area: 25

----------

C# - Operator Overloading

You can redefine or overload most of the built-in operators available in C#. Thus a programmer can use operators with user-defined types as well. Overloaded operators are functions with special names the keyword operator followed by the symbol for the operator being defined. Like any other function, an overloaded operator has a return type and a parameter list.

For example, look at the following function:

  public static Box operator+ (Box b, Box c)
  {
     Box box = new Box();
     box.length = b.length + c.length;
     box.breadth = b.breadth + c.breadth;
     box.height = b.height + c.height;
     return box;
  }

The above function implements the addition operator (+) for a user-defined class Box. It adds the attributes of two Box objects and returns the resultant Box object.
Implementation of Operator Overloading

The following program shows the complete implementation:

  using System;

  namespace OperatorOvlApplication
  {
     class Box
     {
        private double length;      // Length of a box
        private double breadth;     // Breadth of a box
        private double height;      // Height of a box

        public double getVolume()
        {
           return length * breadth * height;
        }
        public void setLength( double len )
        {
           length = len;
        }

        public void setBreadth( double bre )
        {
           breadth = bre;
        }

        public void setHeight( double hei )
        {
           height = hei;
        }
        // Overload + operator to add two Box objects.
        public static Box operator+ (Box b, Box c)
        {
           Box box = new Box();
           box.length = b.length + c.length;
           box.breadth = b.breadth + c.breadth;
           box.height = b.height + c.height;
           return box;
        }

     }

     class Tester
     {
        static void Main(string[] args)
        {
           Box Box1 = new Box();         // Declare Box1 of type Box
           Box Box2 = new Box();         // Declare Box2 of type Box
           Box Box3 = new Box();         // Declare Box3 of type Box
           double volume = 0.0;          // Store the volume of a box here

           // box 1 specification
           Box1.setLength(6.0);
           Box1.setBreadth(7.0);
           Box1.setHeight(5.0);

           // box 2 specification
           Box2.setLength(12.0);
           Box2.setBreadth(13.0);
           Box2.setHeight(10.0);

           // volume of box 1
           volume = Box1.getVolume();
           Console.WriteLine("Volume of Box1 : {0}", volume);

           // volume of box 2
           volume = Box2.getVolume();
           Console.WriteLine("Volume of Box2 : {0}", volume);

           // Add two object as follows:
           Box3 = Box1 + Box2;

           // volume of box 3
           volume = Box3.getVolume();
           Console.WriteLine("Volume of Box3 : {0}", volume);
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Volume of Box1 : 210
  Volume of Box2 : 1560
  Volume of Box3 : 5400

Overloadable and Non-Overloadable Operators

The following table describes the overload ability of the operators in C#:

  +----------------------+---------------------------------------------+
  | Operators            | Description                                 |
  +----------------------+---------------------------------------------+
  | +, -, !, ~, ++, --   | These unary operators take one operand and  |
  |                      | can be overloaded.                          |
  +----------------------+---------------------------------------------+
  | +, -, *, /, %        | These binary operators take one operand and |
  |                      | can be overloaded.                          |
  +----------------------+---------------------------------------------+
  | ==, !=, <, >, <=, >= | The comparison operators can be overloaded  |
  +----------------------+---------------------------------------------+
  | &&, ||               | The conditional logical operators cannot be |
  |                      | overloaded directly.                        |
  +----------------------+---------------------------------------------+
  | +=, -=, *=, /=, %=   | The assignment operators cannot be          |
  |                      | overloaded.                                 |
  +----------------------+---------------------------------------------+
  | =, ., ?:, ->, new,   | These operators cannot be overloaded.       |
  | is, sizeof, typeof   |                                             |
  +----------------------+---------------------------------------------+

Example:

In the light of the above discussions, let us extend the preceding example, and overload few more operators:

  using System;

  namespace OperatorOvlApplication
  {
      class Box
      {
         private double length;      // Length of a box
         private double breadth;     // Breadth of a box
         private double height;      // Height of a box

         public double getVolume()
         {
           return length * breadth * height;
         }
        public void setLength( double len )
        {
            length = len;
        }

        public void setBreadth( double bre )
        {
            breadth = bre;
        }

        public void setHeight( double hei )
        {
            height = hei;
        }
        // Overload + operator to add two Box objects.
        public static Box operator+ (Box b, Box c)
        {
            Box box = new Box();
            box.length = b.length + c.length;
            box.breadth = b.breadth + c.breadth;
            box.height = b.height + c.height;
            return box;
        }

        public static bool operator == (Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length == rhs.length && lhs.height == rhs.height
               && lhs.breadth == rhs.breadth)
            {
                status = true;
            }
            return status;
        }
        public static bool operator !=(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length != rhs.length || lhs.height != rhs.height
                || lhs.breadth != rhs.breadth)
            {
                status = true;
            }
            return status;
        }
        public static bool operator <(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length < rhs.length && lhs.height
                < rhs.height && lhs.breadth < rhs.breadth)
            {
                status = true;
            }
            return status;
        }

        public static bool operator >(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length > rhs.length && lhs.height
                > rhs.height && lhs.breadth > rhs.breadth)
            {
                status = true;
            }
            return status;
        }

        public static bool operator <=(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length <= rhs.length && lhs.height
                <= rhs.height && lhs.breadth <= rhs.breadth)
            {
                status = true;
            }
            return status;
        }

        public static bool operator >=(Box lhs, Box rhs)
        {
            bool status = false;
            if (lhs.length >= rhs.length && lhs.height
               >= rhs.height && lhs.breadth >= rhs.breadth)
            {
                status = true;
            }
            return status;
        }
        public override string ToString()
        {
            return String.Format("({0}, {1}, {2})", length, breadth, height);
        }

     }

     class Tester
     {
        static void Main(string[] args)
        {
          Box Box1 = new Box();          // Declare Box1 of type Box
          Box Box2 = new Box();          // Declare Box2 of type Box
          Box Box3 = new Box();          // Declare Box3 of type Box
          Box Box4 = new Box();
          double volume = 0.0;   // Store the volume of a box here

          // box 1 specification
          Box1.setLength(6.0);
          Box1.setBreadth(7.0);
          Box1.setHeight(5.0);

          // box 2 specification
          Box2.setLength(12.0);
          Box2.setBreadth(13.0);
          Box2.setHeight(10.0);

         //displaying the Boxes using the overloaded ToString():
          Console.WriteLine("Box 1: {0}", Box1.ToString());
          Console.WriteLine("Box 2: {0}", Box2.ToString());

          // volume of box 1
          volume = Box1.getVolume();
          Console.WriteLine("Volume of Box1 : {0}", volume);

          // volume of box 2
          volume = Box2.getVolume();
          Console.WriteLine("Volume of Box2 : {0}", volume);

          // Add two object as follows:
          Box3 = Box1 + Box2;
          Console.WriteLine("Box 3: {0}", Box3.ToString());
          // volume of box 3
          volume = Box3.getVolume();
          Console.WriteLine("Volume of Box3 : {0}", volume);

          //comparing the boxes
          if (Box1 > Box2)
            Console.WriteLine("Box1 is greater than Box2");
          else
            Console.WriteLine("Box1 is  greater than Box2");
          if (Box1 < Box2)
            Console.WriteLine("Box1 is less than Box2");
          else
            Console.WriteLine("Box1 is not less than Box2");
          if (Box1 >= Box2)
            Console.WriteLine("Box1 is greater or equal to Box2");
          else
            Console.WriteLine("Box1 is not greater or equal to Box2");
          if (Box1 <= Box2)
            Console.WriteLine("Box1 is less or equal to Box2");
          else
            Console.WriteLine("Box1 is not less or equal to Box2");
          if (Box1 != Box2)
            Console.WriteLine("Box1 is not equal to Box2");
          else
            Console.WriteLine("Box1 is not greater or equal to Box2");
          Box4 = Box3;
          if (Box3 == Box4)
            Console.WriteLine("Box3 is equal to Box4");
          else
            Console.WriteLine("Box3 is not equal to Box4");

          Console.ReadKey();
        }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Box 1: (6, 7, 5)
  Box 2: (12, 13, 10)
  Volume of Box1 : 210
  Volume of Box2 : 1560
  Box 3: (18, 20, 15)
  Volume of Box3 : 5400
  Box1 is not greater than Box2
  Box1 is less than Box2
  Box1 is not greater or equal to Box2
  Box1 is less or equal to Box2
  Box1 is not equal to Box2
  Box3 is equal to Box4

----------

C# - Interfaces

An interface is defined as a syntactical contract that all the classes inheriting the interface should follow. The interface defines the 'what' part of the syntactical contract and the deriving classes define the 'how' part of the syntactical contract.

Interfaces define properties, methods and events, which are the members of the interface. Interfaces contain only the declaration of the members. It is the responsibility of the deriving class to define the members. It often helps in providing a standard structure that the deriving classes would follow.

Abstract classes to some extent serve the same purpose, however, they are mostly used when only few methods are to be declared by the base class and the deriving class implements the functionalities.
Declaring Interfaces

Interfaces are declared using the interface keyword. It is similar to class declaration. Interface statements are public by default. Following is an example of an interface declaration:

  public interface ITransactions
  {
     // interface members
     void showTransaction();
     double getAmount();
  }

Example

The following example demonstrates implementation of the above interface:

  using System.Collections.Generic;
  using System.Linq;
  using System.Text;

  namespace InterfaceApplication
  {

     public interface ITransactions
     {
        // interface members
        void showTransaction();
        double getAmount();
     }
     public class Transaction : ITransactions
     {
        private string tCode;
        private string date;
        private double amount;
        public Transaction()
        {
           tCode = " ";
           date = " ";
           amount = 0.0;
        }
        public Transaction(string c, string d, double a)
        {
           tCode = c;
           date = d;
           amount = a;
        }
        public double getAmount()
        {
           return amount;
        }
        public void showTransaction()
        {
           Console.WriteLine("Transaction: {0}", tCode);
           Console.WriteLine("Date: {0}", date);
           Console.WriteLine("Amount: {0}", getAmount());

        }

     }
     class Tester
     {
        static void Main(string[] args)
        {
           Transaction t1 = new Transaction("001", "8/10/2012", 78900.00);
           Transaction t2 = new Transaction("002", "9/10/2012", 451900.00);
           t1.showTransaction();
           t2.showTransaction();
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Transaction: 001
  Date: 8/10/2012
  Amount: 78900
  Transaction: 002
  Date: 9/10/2012
  Amount: 451900

----------

C# - Namespaces

A namespace is designed for providing a way to keep one set of names separate from another. The class names declared in one namespace will not conflict with the same class names declared in another.


Defining a Namespace

A namespace definition begins with the keyword namespace followed by the namespace name as follows:

  namespace namespace_name
  {
     // code declarations
  }

To call the namespace-enabled version of either function or variable, prepend the namespace name as follows:

  namespace_name.item_name;

The following program demonstrates use of namespaces:

  using System;
  namespace first_space
  {
     class namespace_cl
     {
        public void func()
        {
           Console.WriteLine("Inside first_space");
        }
     }
  }
  namespace second_space
  {
     class namespace_cl
     {
        public void func()
        {
           Console.WriteLine("Inside second_space");
        }
     }
  }
  class TestClass
  {
     static void Main(string[] args)
     {
        first_space.namespace_cl fc = new first_space.namespace_cl();
        second_space.namespace_cl sc = new second_space.namespace_cl();
        fc.func();
        sc.func();
        Console.ReadKey();
     }
  }

When the above code is compiled and executed, it produces the following result:

  Inside first_space
  Inside second_space


The using Keyword

The using keyword states that the program is using the names in the given namespace. For example, we are using the System namespace in our programs. The class Console is defined there. We just write:

  Console.WriteLine ("Hello there");

We could have written the fully qualified name as:

  System.Console.WriteLine("Hello there");

You can also avoid prepending of namespaces with the using namespace directive. This directive tells the compiler that the subsequent code is making use of names in the specified namespace. The namespace is thus implied for the following code:

Let us rewrite our preceding example, with using directive:

  using System;
  using first_space;
  using second_space;

  namespace first_space
  {
     class abc
     {
        public void func()
        {
           Console.WriteLine("Inside first_space");
        }
     }
  }
  namespace second_space
  {
     class efg
     {
        public void func()
        {
           Console.WriteLine("Inside second_space");
        }
     }
  }
  class TestClass
  {
     static void Main(string[] args)
     {
        abc fc = new abc();
        efg sc = new efg();
        fc.func();
        sc.func();
        Console.ReadKey();
     }
  }

When the above code is compiled and executed, it produces the following result:

  Inside first_space
  Inside second_space


Nested Namespaces

Namespaces can be nested where you can define one namespace inside another namespace as follows:

  namespace namespace_name1
  {
     // code declarations
     namespace namespace_name2
     {
       // code declarations
     }
  }

You can access members of nested namespace by using the dot (.) operator as follows:

  using System;
  using first_space;
  using first_space.second_space;

  namespace first_space
  {
     class abc
     {
        public void func()
        {
           Console.WriteLine("Inside first_space");
        }
     }
     namespace second_space
     {
        class efg
        {
           public void func()
           {
              Console.WriteLine("Inside second_space");
           }
        }
     }
  }

  class TestClass
  {
     static void Main(string[] args)
     {
        abc fc = new abc();
        efg sc = new efg();
        fc.func();
        sc.func();
        Console.ReadKey();
     }
  }

When the above code is compiled and executed, it produces the following result:

  Inside first_space
  Inside second_space

----------

C# - Preprocessor Directives

The preprocessors directives give instruction to the compiler to preprocess the information before actual compilation starts.

All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Preprocessor directives are not statements, so they do not end with a semicolon (;).

C# compiler does not have a separate preprocessor; however, the directives are processed as if there was one. In C# the preprocessor directives are used to help in conditional compilation. Unlike C and C++ directives, they are not used to create macros. A preprocessor directive must be the only instruction on a line.


List of Preprocessor Directives in C#

The following table lists the preprocessor directives available in C#:

  +------------+-------------------------------------------------------+
  | Directive  | Description.                                          |
  +------------+-------------------------------------------------------+
  | #define    | It defines a sequence of characters, called symbol.   |
  +------------+-------------------------------------------------------+
  | #undef     | It allows you to undefine a symbol.                   |
  +------------+-------------------------------------------------------+
  | #if        | It allows testing a symbol or symbols to see if they  |
  |            | evaluate to true.                                     |
  +------------+-------------------------------------------------------+
  | #else      | It allows to create a compound conditional directive, |
  |            | along with #if.                                       |
  +------------+-------------------------------------------------------+
  | #elif      | It allows creating a compound conditional directive.  |
  +------------+-------------------------------------------------------+
  | #endif     | Specifies the end of a conditional directive.         |
  +------------+-------------------------------------------------------+
  | #line      | It lets you modify the compiler's line number and     |
  |            | (optionally) the file name output for errors and      |
  |            | warnings.                                             |
  +------------+-------------------------------------------------------+
  | #error     | It allows generating an error from a specific         |
  |            | location in your code.                                |
  +------------+-------------------------------------------------------+
  | #warning   | It allows generating a level one warning from a       |
  |            | specific location in your code.                       |
  +------------+-------------------------------------------------------+
  | #region    | It lets you specify a block of code that you can      |
  |            | expand or collapse when using the outlining feature   |
  |            | of the Visual Studio Code Editor.                     |
  +------------+-------------------------------------------------------+
  | #endregion | It marks the end of a #region block.                  |
  +------------+-------------------------------------------------------+


The #define Preprocessor

The #define preprocessor directive creates symbolic constants.

#define lets you define a symbol, such that, by using the symbol as the expression passed to the #if directive, the expression will evaluate to true. Its syntax is as follows:

  #define symbol

The following program illustrates this:

  #define PI
  using System;
  namespace PreprocessorDAppl
  {
     class Program
     {
        static void Main(string[] args)
        {
           #if (PI)
              Console.WriteLine("PI is defined");
           #else
              Console.WriteLine("PI is not defined");
           #endif
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  PI is defined


Conditional Directives

You can use the #if directive to create a conditional directive. Conditional directives are useful for testing a symbol or symbols to see if they evaluate to true. If they do evaluate to true, the compiler evaluates all the code between the #if and the next directive.

Syntax for conditional directive is:

  #if symbol [operator symbol]...

Where, symbol is the name of the symbol you want to test. You can also use true and false or prepend the symbol with the negation operator.

The operator symbol is the operator used for evaluating the symbol. Operators could be either of the following:

    == (equality)
    != (inequality)
    && (and)
    || (or)

You can also group symbols and operators with parentheses. Conditional directives are used for compiling code for a debug build or when compiling for a specific configuration. A conditional directive beginning with a #if directive must explicitly be terminated with a #endif directive.

The following program demonstrates use of conditional directives:

  #define DEBUG
  #define VC_V10
  using System;
  public class TestClass
  {
     public static void Main()
     {

        #if (DEBUG && !VC_V10)
           Console.WriteLine("DEBUG is defined");
        #elif (!DEBUG && VC_V10)
           Console.WriteLine("VC_V10 is defined");
        #elif (DEBUG && VC_V10)
           Console.WriteLine("DEBUG and VC_V10 are defined");
        #else
           Console.WriteLine("DEBUG and VC_V10 are not defined");
        #endif
        Console.ReadKey();
     }
  }

When the above code is compiled and executed, it produces the following result:

  DEBUG and VC_V10 are defined

----------

C# - Regular Expressions

A regular expression is a pattern that could be matched against an input text. The .Net framework provides a regular expression engine that allows such matching. A pattern consists of one or more character literals, operators, or constructs.
Constructs for Defining Regular Expressions

There are various categories of characters, operators, and constructs that lets you to define regular expressions. Click the follwoing links to find these constructs.

  - Character escapes
  - Character classes
  - Anchors
  - Grouping constructs
  - Quantifiers
  - Backreference constructs
  - Alternation constructs
  - Substitutions
  - Miscellaneous constructs


The Regex Class

The Regex class is used for representing a regular expression.

  The Regex class has the following commonly used methods:

  +-----+--------------------------------------------------------------+
  | S.N | Methods & Description                                        |
  +-----+--------------------------------------------------------------+
  | 1   | public bool IsMatch( string input )                          |
  |     |                                                              |
  |     | Indicates whether the regular expression specified in the    |
  |     | Regex constructor finds a match in a specified input string. |
  +-----+--------------------------------------------------------------+
  | 2   | public bool IsMatch( string input, int startat )             |
  |     |                                                              |
  |     | Indicates whether the regular expression specified in the    |
  |     | Regex constructor finds a match in the specified input       |
  |     | string, beginning at the specified starting position in the  |
  |     | string.                                                      |
  +-----+--------------------------------------------------------------+
  | 3   | public static bool IsMatch( string input, string pattern )   |
  |     |                                                              |
  |     | Indicates whether the specified regular expression finds a   |
  |     | match in the specified input string.                         |
  +-----+--------------------------------------------------------------+
  | 4   | public MatchCollection Matches( string input )               |
  |     |                                                              |
  |     | Searches the specified input string for all occurrences of a |
  |     | regular expression.                                          |
  +-----+--------------------------------------------------------------+
  | 5   | public string Replace( string input, string replacement )    |
  |     |                                                              |
  |     | In a specified input string, replaces all strings that match |
  |     | a regular expression pattern with a specified replacement    |
  |     | string.                                                      |
  +-----+--------------------------------------------------------------+
  | 6   | public string[] Split( string input )                        |
  |     |                                                              |
  |     | Splits an input string into an array of substrings at the    |
  |     | positions defined by a regular expression pattern specified  |
  |     | in the Regex constructor.                                    |
  +-----+--------------------------------------------------------------+

For the complete list of methods and properties, please read the Microsoft documentation on C#.

Example 1

The following example matches words that start with 'S':

  using System;
  using System.Text.RegularExpressions;

  namespace RegExApplication
  {
     class Program
     {
        private static void showMatch(string text, string expr)
        {
           Console.WriteLine("The Expression: " + expr);
           MatchCollection mc = Regex.Matches(text, expr);
           foreach (Match m in mc)
           {
              Console.WriteLine(m);
           }
        }
        static void Main(string[] args)
        {
           string str = "A Thousand Splendid Suns";

           Console.WriteLine("Matching words that start with 'S': ");
           showMatch(str, @"\bS\S*");
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Matching words that start with 'S':
  The Expression: \bS\S*
  Splendid
  Suns

Example 2

The following example matches words that start with 'm' and ends with 'e':

  using System;
  using System.Text.RegularExpressions;

  namespace RegExApplication
  {
     class Program
     {
        private static void showMatch(string text, string expr)
        {
           Console.WriteLine("The Expression: " + expr);
           MatchCollection mc = Regex.Matches(text, expr);
           foreach (Match m in mc)
           {
              Console.WriteLine(m);
           }
        }
        static void Main(string[] args)
        {
           string str = "make maze and manage to measure it";

           Console.WriteLine("Matching words start with 'm' and ends with 'e':");
           showMatch(str, @"\bm\S*e\b");
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Matching words start with 'm' and ends with 'e':
  The Expression: \bm\S*e\b
  make
  maze
  manage
  measure

Example 3

This example replaces extra white space:

  using System;
  using System.Text.RegularExpressions;

  namespace RegExApplication
  {
     class Program
     {
        static void Main(string[] args)
        {
           string input = "Hello   World   ";
           string pattern = "\\s+";
           string replacement = " ";
           Regex rgx = new Regex(pattern);
           string result = rgx.Replace(input, replacement);

           Console.WriteLine("Original String: {0}", input);
           Console.WriteLine("Replacement String: {0}", result);
           Console.ReadKey();
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  Original String: Hello   World
  Replacement String: Hello World


C# - Character Escapes Regular Expressions

These are basically the special characters or escape characters. The backslash character (\) in a regular expression indicates that the character that follows it either is a special character or should be interpreted literally.

The following table lists the escape characters:

  +-------+-------------------------------------------------+----------+
  | Esc.  | Description                                     | Pattern  | 
  |       | Matches                                         |          |
  +-------+-------------------------------------------------+----------+
  | \a    |Matches a bell character, \u0007.                |\a        |
  |       |                                                 |          |
  |       |"\u0007" in "Warning!" + '\u0007'                |          |
  +-------+-------------------------------------------------+----------+
  | \b    |In a character class, matches a backspace, \u0008|[\b]{3,}  |
  |       |                                                 |          |
  |       |"\b\b\b\b" in "\b\b\b\b"                         |          |
  +-------+-------------------------------------------------+----------+
  | \t    |Matches a tab, \u0009.                           |(\w+)\t   |
  |       |                                                 |          |
  |       |"Name\t", "Addr\t" in "Name\tAddr\t"             |          |
  +-------+-------------------------------------------------+----------+
  | \r    |Matches a carriage return, \u000D. (\r is not    |\r\n(\w+) |
  |       |equivalent to the newline character, \n.)        |          |
  |       |                                                 |          |
  |       |"\r\nHello" in "\r\Hello\nWorld."                |          |
  +-------+-------------------------------------------------+----------+
  | \v    |Matches a vertical tab, \u000B.                  |[\v]{2,}  |
  |       |                                                 |          |
  |       |"\v\v\v" in "\v\v\v"                             |          |
  +-------+-------------------------------------------------+----------+
  | \f    |Matches a form feed, \u000C.                     |[\f]{2,}  |
  |       |                                                 |          |
  |       |"\f\f\f" in "\f\f\f"                             |          |
  +-------+-------------------------------------------------+----------+
  | \n    |Matches a new line, \u000A.                      |\r\n(\w+) |
  |       |                                                 |          |
  |       |"\r\nHello" in "\r\Hello\nWorld."                |          |
  +-------+-------------------------------------------------+----------+
  | \e    |Matches an escape, \u001B.                       |\e        |
  |       |                                                 |          |
  |       |"\x001B" in "\x001B"                             |          |
  +-------+-------------------------------------------------+----------+
  | \nnn  |Uses octal representation to specify a character |\w\040\w  |
  |       |(nnn consists of up to three digits).            |          |
  |       |                                                 |          |
  |       |"a b", "c d" in "a bc d"                         |          |
  +-------+-------------------------------------------------+----------+
  | \xnn  |Uses hexadecimal representation to specify a     |\w\x20\w  |
  |       |character (nn consists of exactly two digits).   |          |
  |       |                                                 |          |
  |       |"a b", "c d" in "a bc d"                         |          |
  +-------+-------------------------------------------------+----------+
  | \cX   |Matches the ASCII control character that is      |\cC       |
  | \cx   |specified by X or x, where X or x is the letter  |          |
  |       |of the control character.                        |          |
  |       |                                                 |          |
  |       |"\x0003" in "\x0003" (Ctrl-C)                    |          |
  +-------+-------------------------------------------------+----------+
  | \unnnn|Matches a Unicode character by using hexadecimal |\w\u0020\w|
  |       |representation (exactly four digits, as          |          |
  |       |represented by nnnn).                            |          |
  |       |                                                 |          |
  |       |"a b", "c d" in "a bc d"                         |          |
  +-------+-------------------------------------------------+----------+
  | \     |When followed by a character that is not         |\+, \* .. |
  |       |recognized as an escaped character, matches      |          |
  |       |that character.                                  |          |
  |       |                                                 |          |
  |       |\d+[\+-x\*]\d+\d+[\+-x\*\d+                      |          |
  |       |"2+2" and "3*9" in "(2+2) * 3*9"                 |          |
  +-------+-------------------------------------------------+----------+


C# - Character Classes Regular Expressions

A character class matches any one of a set of characters. The following table describes the character classes:

  +-------------------+---------------------------------------+--------+
  | Character class   | Description                           |Pattern |
  |                   | Matches                               |        |
  +-------------------+---------------------------------------+--------+
  | [character_group] |Matches any single character in        |[mn]    |
  |                   |character_group. By default, the       |        |
  |                   |match is case-sensitive.               |        |
  |                   |                                       |        |
  |                   |"m" in "mat" "m", "n" in "moon"        |        |
  +-------------------+---------------------------------------+--------+
  | [^character_group]|Negation: Matches any single character |[^aei]  |
  |                   |that is not in character_group. By     |        |
  |                   |default, characters incharacter_group  |        |
  |                   |are case-sensitive.                    |        |
  |                   |                                       |        |
  |                   |"v", "l" in "avail"                    |        |
  +-------------------+---------------------------------------+--------+
  | [ first - last ]  |Character range: Matches any single    |(\w+)\t |
  |                   |character in the range from first      |        |
  |                   |to last.                               |        |
  |                   |                                       |        |
  |                   |"Name\t", "Addr\t" in "Name\tAddr\t"   |        |
  +-------------------+---------------------------------------+--------+
  | .                 |Wildcard: Matches any single character |.       |
  |                   |except \n.                             |        |
  |                   |                                       |        |
  |                   |a.e "ave" in "have" "ate" in "mate"    |\p{Lu}  |
  +-------------------+---------------------------------------+--------+
  | \p{ name }        |Matches any single character in the    |        |
  |                   |Unicode general category or named block|        |
  |                   |specified by name.                     |        |
  |                   |                                       |        |
  |                   |"C", "L" in "City Lights"              |\P{Lu}  |
  +-------------------+---------------------------------------+--------+
  | \P{ name }        |Matches any single character that is   |        |
  |                   |not in the Unicode general category or |        |
  |                   |named block specified by name.         |        |
  |                   |                                       |        |
  |                   |"i", "t", "y" in "City"                |        |
  +-------------------+---------------------------------------+--------+
  | \w                |Matches any word character.            |\w      |
  |                   |                                       |        |
  |                   |"R", "o", "m" and "1" in "Room#1"      |        |
  +-------------------+---------------------------------------+--------+
  | \W                |Matches any non-word character.        |\W      |
  |                   |                                       |        |
  |                   |"#" in "Room#1"                        |        |
  +-------------------+---------------------------------------+--------+
  | \s                |Matches any white-space character.     |\w\s    |
  |                   |                                       |        |
  |                   |"D " in "ID A1.3"                      |        |
  +-------------------+---------------------------------------+--------+
  | \S                |Matches any non-white-space character. |\s\S    |
  |                   |                                       |        |
  |                   |" _" in "int __ctr"                    |        |
  +-------------------+---------------------------------------+--------+
  | \d                |Matches any decimal digit.             |\d      |
  |                   |                                       |        |
  |                   |"4" in "4 = IV"                        |        |
  +-------------------+---------------------------------------+--------+
  | \D                |Matches any character other than a     |\D      |
  |                   |decimal digit.                         |        |
  |                   |                                       |        |
  |                   |" ", "=", " ", "I", "V" in "4 = IV"    |        |
  +-------------------+---------------------------------------+--------+


C# - Anchors Regular Expressions

Anchors allow a match to succeed or fail depending on the current position in the string. The following table lists the anchors:

  +------+-------------------------------------------------+-----------+
  | Anc- | Description                                     | Pattern   |
  | hor  | Matches                                         |           |
  +------+-------------------------------------------------+-----------+
  | ^    | The match must start at the beginning of the    | ^\d{3}    |
  |      | string or line.                                 |           |
  |      |                                                 |           |
  |      | "567" in "567-777-"                             |           |
  +------+-------------------------------------------------+-----------+
  | $    | The match must occur at the end of the string   | -\d{4}$   |
  |      | or before \n at the end of the line or string.  |           |
  |      |                                                 |           |
  |      | "-2012" in "8-12-2012"                          |           |
  +------+-------------------------------------------------+-----------+
  | \A   | The match must occur at the start of the string.| \A\w{3}   |
  |      |                                                 |           |
  |      | "Code" in "Code-007-"                           |           |
  +------+-------------------------------------------------+-----------+
  | \Z   | The match must occur at the end of the string or| -\d{3}\Z  |
  |      | before \n at the end of the string.             |           |
  |      |                                                 |           |
  |      | "-007" in "Bond-901-007"                        |           |
  +------+-------------------------------------------------+-----------+
  | \z   | The match must occur at the end of the string.  | -\d{3}\z  | 
  |      |                                                 |           |
  |      | "-333" in "-901-333"                            |           |
  +------+-------------------------------------------------+-----------+
  | \G   | The match must occur at the point where the     | \\G\(\d\) |  
  |      | previous match ended.                           |           |
  |      |                                                 |           |
  |      | "(1)", "(3)", "(5)" in "(1)(3)(5)[7](9)"        |           |
  +------+-------------------------------------------------+-----------+
  | \b   | The match must occur on a boundary between a    | \w        |
  |      | \w (alphanumeric) and a \W(nonalphanumeric)     |           |
  |      | character.                                      |           |
  |      |                                                 |           |
  |      | "R", "o", "m" and "1" in "Room#1"               |           |
  +------+-------------------------------------------------+-----------+
  | \B   |  The match must not occur on a \b boundary.     | \Bend\w*\b|   
  |      |                                                 |           |
  |      | "ends", "ender" in "end sends endure lender"    |           |
  +------+-------------------------------------------------+-----------+


C# - Grouping Constructs Regular Expressions

Grouping constructs delineate sub-expressions of a regular expression and capture substrings of an input string. The following table lists the grouping constructs:

  +--------------------------------------------------------------------+
  | Grouping construct                                                 |
  | Description                                                        |
  | Matches                                                            |
  | Pattern                                                            |
  +--------------------------------------------------------------------+
  | ( subexpression )                                                  |
  |                                                                    |
  | Captures the matched subexpression and assigns                     |
  | it a zero-based ordinal number.                                    |
  |                                                                    |
  | (\w)\1                                                             |
  |                                                                    |
  | "ee" in "deep"                                                     |
  +--------------------------------------------------------------------+
  |  (?<name>subexpression)                                            |
  |                                                                    |
  |  Captures the matched subexpression into a named                   |
  |  group.                                                            |
  |                                                                    |
  |  (?<double>\w)\k<double>                                           |
  |                                                                    |
  |  "ee" in "deep"                                                    |
  +--------------------------------------------------------------------+
  | (?<name1-name2>subexpression)                                      |
  |                                                                    |
  | Defines a balancing group definition.                              |
  |                                                                    |
  | (((?'Open'\()[^\(\)]*)+((?'Close-Open'\))[^\(\)]*)+)*(?(Open)(?!))$|   
  |                                                                    |
  | "((1-3)*(3-1))" in "3+2^((1-3)*(3-1))"                             |
  +--------------------------------------------------------------------+
  | (?:subexpression)                                                  |
  |                                                                    |
  | Defines a noncapturing group.                                      |
  |                                                                    |
  | Write(?:Line)?                                                     |
  |                                                                    |
  | "WriteLine" in "Console.WriteLine()"                               |
  +--------------------------------------------------------------------+
  | (?imnsx-imnsx:subexpression)                                       |
  |                                                                    |
  | Applies or disables the specified options within subexpression.    |
  |                                                                    |
  | A\d{2}(?i:\w+)\b                                                   |
  |                                                                    |
  | "A12xl", "A12XL" in "A12xl A12XL a12xl"                            |
  +--------------------------------------------------------------------+
  | (?=subexpression)                                                  |
  |                                                                    |
  | Zero-width positive lookahead assertion.                           |
  |                                                                    |
  | \w+(?=\.)                                                          |
  |                                                                    |
  | "is", "ran", and "out" in "He is. The dog ran. The sun is out."    |
  +--------------------------------------------------------------------+
  | (?!subexpression)                                                  |
  |                                                                    |
  | Zero-width negative lookahead assertion.                           |
  |                                                                    |
  | \b(?!un)\w+\b                                                      |
  |                                                                    |
  | "sure", "used" in "unsure sure unity used"                         |
  +--------------------------------------------------------------------+
  | (?<=subexpression)                                                 |
  |                                                                    |
  | Zero-width positive lookbehind assertion.                          |
  |                                                                    |
  | (?<=19)\d{2}\b                                                     |
  |                                                                    |
  | "51", "03" in "1851 1999 1950 1905 2003"                           |
  +--------------------------------------------------------------------+
  | (?<!subexpression)                                                 |
  |                                                                    |
  | Zero-width negative lookbehind assertion.                          |
  |                                                                    |
  | (?<!19)\d{2}\b                                                     |
  |                                                                    |
  | "ends", "ender" in "end sends endure lender"                       |
  +--------------------------------------------------------------------+
  | (?> subexpression)                                                 |
  |                                                                    |
  | Nonbacktracking (or "greedy") subexpression.                       |
  |                                                                    |
  | [13579](?>A+B+)                                                    |
  |                                                                    |
  | "1ABB", "3ABB", and "5AB" in "1ABB 3ABBC 5AB 5AC"                  |
  +--------------------------------------------------------------------+
  

C# - Quantifier Regular Expressions

Quantifiers specify how many instances of the previous element (which can be a character, a group, or a character class) must be present in the input string for a match to occur.

  +------------+-------------------------------------------------------+
  | Quantifier | Description                                           |
  |            |                                                       |
  |            | Pattern   Matches                                     |
  +------------+-------------------------------------------------------+
  | *          | Matches the previous element zero or more times.      |
  |            |                                                       |
  |            | \d*\.\d    ".0", "19.9", "219.9"                      |
  +------------+-------------------------------------------------------+
  | +          | Matches the previous element one or more times.       |
  |            |                                                       |
  |            | "be+"    "bee" in "been", "be" in "bent"              |
  +------------+-------------------------------------------------------+
  | ?          | Matches the previous element zero or one time.        |
  |            |                                                       |
  |            | "rai?n"    "ran", "rain"                              |
  +------------+-------------------------------------------------------+
  | { n }      | Matches the previous element exactly n times.         |
  |            |                                                       |
  |            | ",\d{3}"    ",043" in "1,043.6", ",876", ",543", and  |
  |            |             ",210" in "9,876,543,210"                 |
  +------------+-------------------------------------------------------+
  | { n ,}     | Matches the previous element at least n times.        |
  |            |                                                       |
  |            | "\d{2,}"    "166", "29", "1930"                       |
  +------------+-------------------------------------------------------+
  | { n , m }  | Matches the previous element at least n times,        |
  |            | but no more than m times.                             |
  |            |                                                       |
  |            | "\d{3,5}"    "166", "17668" "19302" in "193024"       |
  +------------+-------------------------------------------------------+
  | *?         | Matches the previous element zero or more times,      |
  |            | but as few times as possible.                         |
  |            |                                                       |
  |            | \d*?\.\d    ".0", "19.9", "219.9"                     |
  +------------+-------------------------------------------------------+
  | +?         | Matches the previous element one or more times,       |
  |            | but as few times as possible.                         |
  |            |                                                       |
  |            | "be+?"    "be" in "been", "be" in "bent"              |
  +------------+-------------------------------------------------------+
  | ??         | Matches the previous element zero or one time,        |
  |            | but as few times as possible.                         |
  |            |                                                       |
  |            | "rai??n"    "ran", "rain"                             |
  +------------+-------------------------------------------------------+
  | { n }?     | Matches the preceding element exactly n times.        |
  |            | ",\d{3}?"    ",043" in "1,043.6", ",876", ",543", and |
  |            |              ",210" in "9,876,543,210"                |
  +------------+-------------------------------------------------------+
  | { n ,}?    | Matches the previous element at least n times,        |
  |            | but as few times as possible.                         |
  |            |                                                       |
  |            | "\d{2,}?"    "166", "29", "1930"                      |
  +------------+-------------------------------------------------------+
  | { n , m }? | Matches the previous element between n and m times,   |
  |            | but as few times as possible.                         |
  |            |                                                       |
  |            | "\d{3,5}?"    "166", "17668" "193", "024" in "193024" |
  +------------+-------------------------------------------------------+


C# Backreference Constructs Regular Expressions

Backreference constructs allow a previously matched sub-expression to be identified subsequently in the same regular expression.

The following table lists these constructs:

  +--------------------------------------------------------------------+
  | Backreference construct    Description    Pattern    Matches       |
  +----------+---------------------------------------------------------+
  | \number  | Backreference. Matches the value of a numbered          |
  |          | subexpression.                                          |
  |          |                                                         |
  |          | (\w)\1                                                  |
  |          |                                                         |
  |          | "ee" in "seek"                                          |
  +----------+---------------------------------------------------------+
  | \k<name> | Named backreference. Matches the value of a named       |
  |          | expression.                                             |
  |          |                                                         |
  |          | (?< char>\w)\k< char>                                   |
  |          |                                                         |
  |          | "ee" in "seek"                                          |
  +----------+---------------------------------------------------------+

Alternation constructs modify a regular expression to enable either/or matching. The following table lists the alternation constructs:

  +--------------------------------------------------------------------+
  | Alternation construct                                              |
  | Description                                                        |
  | Pattern                                                            |
  | Matches                                                            |
  +--------------------------------------------------------------------+
  | Matches any one element separated by the vertical bar (|)          |
  | character.                                                         |
  |                                                                    |
  | th(e|is|at)                                                        |
  |                                                                    |
  | "the", "this" in "this is the day. "                               |
  +--------------------------------------------------------------------+
  | (?(expression)yes|no)                                              |
  |                                                                    |
  | Matches yes if expression matches; otherwise, matches the optional |
  | no part. Expression is interpreted as a zero-width assertion.      |
  |                                                                    |
  | (?(A)A\d{2}\b|\b\d{3}\b)                                           |
  |                                                                    |
  | "A10", "910" in "A10 C103 910"                                     |
  +--------------------------------------------------------------------+
  | (?(name)yes|no)                                                    |
  |                                                                    |
  | Matches yes if the named capture name has a match; otherwise,      |
  | matches the optional no.                                           |
  |                                                                    |
  | (?<quoted>")?(?(quoted).+?"|\S+\s)                                 |
  |                                                                    |
  | Dogs.jpg, "Yiska playing.jpg" in "Dogs.jpg "Yiska playing.jpg""    |
  +--------------------------------------------------------------------+
  


C# - Substitution Regular Expressions

Substitutions are used in replacement patterns. The following table lists the substitutions:

  +-----------+--------------------------------------------------------+
  | Character | Description                                            |
  |           |                                                        |
  |           | Pattern    Replacement pattern                         |
  |           |                                                        |
  |           | Input string    Result string                          |
  +-----------+--------------------------------------------------------+
  | $number   | Substitutes the substring matched by group number.     |
  |           |                                                        |
  |           | \b(\w+)(\s)(\w+)\b  $3$2$1                             |
  |           |                                                        |
  |           | "one two"    "two one"                                 |
  +-----------+--------------------------------------------------------+
  | ${name}   | Substitutes the substring matched by the named         |
  |           | groupname.                                             |
  |           |                                                        |
  |           | \b(?< word1>\w+)(\s)(?< word2>\w+)\b  ${word2} ${word1}|   
  |           | "one two"    "two one"                                 |
  +-----------+--------------------------------------------------------+
  | $$        | Substitutes a literal "$".                             |
  |           |                                                        |
  |           | \b(\d+)\s?USD  $$$1                                    |
  |           | "103 USD"    "$103"                                    |
  +-----------+--------------------------------------------------------+
  | $&        | Substitutes a copy of the whole match.                 |
  |           | (\$*(\d*(\.+\d+)?){1})  **$&                           |
  |           |                                                        |
  |           | "$1.30"    "**$1.30**"                                 |
  +-----------+--------------------------------------------------------+
  | $`        | Substitutes all the text of the input string           |
  |           | before the match.                                      |
  |           |                                                        |
  |           | B+  $`                                                 |
  |           |                                                        |
  |           | "AABBCC"    "AAAACC"                                   |
  +-----------+--------------------------------------------------------+
  | $'        | Substitutes all the text of the input string           |
  |           | after the match.                                       |
  |           |                                                        |
  |           | B+  $'                                                 |
  |           |                                                        |
  |           | "AABBCC"    "AACCCC"                                   |
  +-----------+--------------------------------------------------------+
  | $+        | Substitutes the last group that was captured.          |
  |           |                                                        |
  |           | B+(C+)  $+                                             |
  |           |                                                        |
  |           | "AABBCCDD"    AACCDD                                   |
  +-----------+--------------------------------------------------------+
  | $_        | Substitutes the entire input string.                   |
  |           |                                                        |
  |           | B+  $_                                                 |
  |           |                                                        |
  |           | "AABBCC"    "AAAABBCCCC"                               |
  +-----------+--------------------------------------------------------+


C# - Miscellaneous Constructs Regular Expressions

Following are various miscellaneous constructs:

  +-------------------+------------------------------------------------+
  | Construct         | Definition / Example                           |
  +-------------------+------------------------------------------------+
  | (?imnsx-imnsx)    | Sets or disables options such as case          |
  |                   | insensitivity in the middle of a pattern.      |
  |                   |                                                |
  |                   | \bA(?i)b\w+\b matches "ABA", "Able" in         |
  |                   | "ABA Able Act"                                 |
  +-------------------+------------------------------------------------+
  | (?#comment)       | Inline comment. The comment ends at the first  |
  |                   | closing parenthesis.                           |
  |                   |                                                |
  |                   | \bA(?#Matches words starting with A)\w+\b      |
  +-------------------+------------------------------------------------+
  | #[to end of line] | X-mode comment. The comment starts at an       |
  |                   | unescaped # and continues to the end of the    |
  |                   | line.                                          |
  |                   |                                                |
  |                   | (?x)\bA\w+\b#Matches words starting with A     |
  +-------------------+------------------------------------------------+

----------

C# - Exception Handling

An exception is a problem that arises during the execution of a program. A C# exception is a response to an exceptional circumstance that arises while a program is running, such as an attempt to divide by zero.

Exceptions provide a way to transfer control from one part of a program to another. C# exception handling is built upon four keywords: try, catch, finally and throw.

  - try: A try block identifies a block of code for which particular exceptions will be activated. It's followed by one or more catch blocks.

  - catch: A program catches an exception with an exception handler at the place in a program where you want to handle the problem. The catch keyword indicates the catching of an exception.

  - finally: The finally block is used to execute a given set of statements, whether an exception is thrown or not thrown. For example, if you open a file, it must be closed whether an exception is raised or not.

  - throw: A program throws an exception when a problem shows up. This is done using a throw keyword.

Syntax

Assuming a block will raise and exception, a method catches an exception using a combination of the try and catch keywords. A try/catch block is placed around the code that might generate an exception. Code within a try/catch block is referred to as protected code, and the syntax for using try/catch looks like the following:

  try
  {
     // statements causing exception
  }
  catch( ExceptionName e1 )
  {
     // error handling code
  }
  catch( ExceptionName e2 )
  {
     // error handling code
  }
  catch( ExceptionName eN )
  {
     // error handling code
  }
  finally
  {
     // statements to be executed
  }

You can list down multiple catch statements to catch different type of exceptions in case your try block raises more than one exception in different situations.


Exception Classes in C#

C# exceptions are represented by classes. The exception classes in C# are mainly directly or indirectly derived from the System.Exception class. Some of the exception classes derived from the System.Exception class are the System.ApplicationException and System.SystemException classes.

The System.ApplicationException class supports exceptions generated by application programs. So the exceptions defined by the programmers should derive from this class.

The System.SystemException class is the base class for all predefined system exception.

The following table provides some of the predefined exception classes derived from the Sytem.SystemException class:

  +-----------------------------------+--------------------------------+
  | Exception Class                   | Description                    |
  +-----------------------------------+--------------------------------+
  | System.IO.IOException             | Handles I/O errors.            |
  | System.IndexOutOfRangeException   | Handles errors generated when  |
  |                                   | a method refers to an array    |
  |                                   | index out of range.            |
  +-----------------------------------+--------------------------------+
  | System.ArrayTypeMismatchException | Handles errors generated when  |
  |                                   | type is mismatched with the    |
  |                                   | array type.                    |
  +-----------------------------------+--------------------------------+
  | System.NullReferenceException     | Handles errors generated from  |
  |                                   | deferencing a null object.     |
  +-----------------------------------+--------------------------------+
  | System.DivideByZeroException      | Handles errors generated from  |
  |                                   | dividing a dividend with zero. |
  +-----------------------------------+--------------------------------+
  | System.InvalidCastException       | Handles errors generated       |
  |                                   | during typecasting.            |
  +-----------------------------------+--------------------------------+
  | System.OutOfMemoryException       | Handles errors generated from  |
  |                                   | insufficient free memory.      |
  +-----------------------------------+--------------------------------+
  | System.StackOverflowException     | Handles errors generated from  |
  |                                   | stack overflow.                |
  +-----------------------------------+--------------------------------+


Handling Exceptions

C# provides a structured solution to the exception handling problems in the form of try and catch blocks. Using these blocks the core program statements are separated from the error-handling statements.

These error handling blocks are implemented using the try, catch and finally keywords. Following is an example of throwing an exception when dividing by zero condition occurs:

  using System;
  namespace ErrorHandlingApplication
  {
      class DivNumbers
      {
          int result;
          DivNumbers()
          {
              result = 0;
          }
          public void division(int num1, int num2)
          {
              try
              {
                  result = num1 / num2;
              }
              catch (DivideByZeroException e)
              {
                  Console.WriteLine("Exception caught: {0}", e);
              }
              finally
              {
                  Console.WriteLine("Result: {0}", result);
              }

          }
          static void Main(string[] args)
          {
              DivNumbers d = new DivNumbers();
              d.division(25, 0);
              Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Exception caught: System.DivideByZeroException: Attempted to divide by zero.
  at ...
  Result: 0


Creating User-Defined Exceptions

You can also define your own exception. User-defined exception classes are derived from the ApplicationException class. The following example demonstrates this:

  using System;
  namespace UserDefinedException
  {
     class TestTemperature
     {
        static void Main(string[] args)
        {
           Temperature temp = new Temperature();
           try
           {
              temp.showTemp();
           }
           catch(TempIsZeroException e)
           {
              Console.WriteLine("TempIsZeroException: {0}", e.Message);
           }
           Console.ReadKey();
        }
     }
  }
  public class TempIsZeroException: ApplicationException
  {
     public TempIsZeroException(string message): base(message)
     {
     }
  }
  public class Temperature
  {
     int temperature = 0;
     public void showTemp()
     {
        if(temperature == 0)
        {
           throw (new TempIsZeroException("Zero Temperature found"));
        }
        else
        {
           Console.WriteLine("Temperature: {0}", temperature);
        }
     }
  }

When the above code is compiled and executed, it produces the following result:

  TempIsZeroException: Zero Temperature found


Throwing Objects

You can throw an object if it is either directly or indirectly derived from the System.Exception class. You can use a throw statement in the catch block to throw the present object as:

  Catch(Exception e)
  {
     ...
     Throw e
  }

----------

C# - File I/O

A file is a collection of data stored in a disk with a specific name and a directory path. When a file is opened for reading or writing, it becomes a stream.

The stream is basically the sequence of bytes passing through the communication path. There are two main streams: the input stream and the output stream. The input stream is used for reading data from file (read operation) and the output stream is used for writing into the file (write operation).


C# I/O Classes

The System.IO namespace has various class that are used for performing various operation with files, like creating and deleting files, reading from or writing to a file, closing a file etc.

The following table shows some commonly used non-abstract classes in the System.IO namespace:

  +----------------+---------------------------------------------------+
  | I/O Class      | Description                                       |
  +----------------+---------------------------------------------------+
  | BinaryReader   | Reads primitive data from a binary stream.        |
  | BinaryWriter   | Writes primitive data in binary format.           |
  | BufferedStream | A temporary storage for a stream of bytes.        |
  | Directory      | Helps in manipulating a directory structure.      |
  | DirectoryInfo  | Used for performing operations on directories.    |
  | DriveInfo      | Provides information for the drives.              |
  | File           | Helps in manipulating files.                      |
  | FileInfo       | Used for performing operations on files.          |
  | FileStream     | Used to read from and write to any location.      |
  | MemoryStream   | Used for random access to streamed data in memory.|
  | Path           | Performs operations on path information.          |
  | StreamReader   | Used for reading characters from a byte stream.   |
  | StreamWriter   | Is used for writing characters to a stream.       |
  | StringReader   | Is used for reading from a string buffer.         |
  | StringWriter   | Is used for writing into a string buffer.         |
  +----------------+---------------------------------------------------+


The FileStream Class

The FileStream class in the System.IO namespace helps in reading from, writing to and closing files. This class derives from the abstract class Stream.

You need to create a FileStream object to create a new file or open an existing file. The syntax for creating a FileStream object is as follows:

  FileStream <object_name> = new FileStream( 
                                     <file_name>,
                                     <FileMode Enumerator>, 
                                     <FileAccess Enumerator>, 
                                     <FileShare Enumerator>
                                 );

For example, for creating a FileStream object F for reading a file named sample.txt:

  FileStream F = new FileStream(
                         "sample.txt", 
                         FileMode.Open, 
                         FileAccess.Read, 
                         FileShare.Read
                 );

  +-----------+--------------------------------------------------------+
  | Parameter | Description                                            |
  +-----------+--------------------------------------------------------+
  | FileMode  | The FileMode enumerator defines various methods for    |
  |           | opening files. The members of the FileMode enumerator  |
  |           | are:                                                   |
  |           |                                                        |
  |           | Append: It opens an existing file and puts cursor at   |
  |           | the end of file, or creates the file, if the file does |
  |           | not exist.                                             |
  |           |                                                        |
  |           | Create: It creates a new file.                         |
  |           |                                                        |
  |           | CreateNew: It specifies to the operating system, that  |
  |           | it should create a new file.                           |
  |           |                                                        |
  |           | Open: It opens an existing file.                       |
  |           |                                                        |
  |           | OpenOrCreate: It specifies to the operating system that|
  |           | it should open a file if it exists, otherwise it should|
  |           | create a new file.                                     |
  |           |                                                        |
  |           | Truncate: It opens an existing file and truncates its  |
  |           | size to zero bytes.                                    |
  +-----------+--------------------------------------------------------+
  | FileAccess| FileAccess enumerators have members:                   |
  |           | Read, ReadWrite and Write.                             |
  +-----------+--------------------------------------------------------+
  | FileShare | FileShare enumerators have the following members:      |
  |           |                                                        |
  |           | Inheritable: It allows a file handle to pass           |
  |           | inheritance to the child processes                     |
  |           |                                                        |
  |           | None: It declines sharing of the current file          |
  |           |                                                        |
  |           | Read: It allows opening the file for reading           |
  |           |                                                        |
  |           | ReadWrite: It allows opening the file for reading and  |
  |           | writing                                                |
  |           |                                                        |
  |           | Write: It allows opening the file for writing          |
  +-----------+--------------------------------------------------------+

Example:

The following program demonstrates use of the FileStream class:

  using System;
  using System.IO;

  namespace FileIOApplication
  {
      class Program
      {
          static void Main(string[] args)
          {
              FileStream F = new FileStream("test.dat",
              FileMode.OpenOrCreate, FileAccess.ReadWrite);

              for (int i = 1; i <= 20; i++)
              {
                  F.WriteByte((byte)i);
              }

              F.Position = 0;

              for (int i = 0; i <= 20; i++)
              {
                  Console.Write(F.ReadByte() + " ");
              }
              F.Close();
              Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 -1


Advanced File Operations in C#

The preceding example provides simple file operations in C#. However, to utilize the immense powers of C# System.IO classes, you need to know the commonly used properties and methods of these classes.

We will discuss these classes and the operations they perform, in the following sections. Please click the links provided to get to the individual sections:

Topic and Description

Reading from and Writing into Text files

It involves reading from and writing into text files. The StreamReader and StreamWriter class helps to accomplish it.

Reading from and Writing into Binary files

It involves reading from and writing into binary files. The BinaryReader and BinaryWriter class helps to accomplish this.

Manipulating the Windows file system

It gives a C# programamer the ability to browse and locate Windows files and directories.

----------

C# - Reading from and Writing to Text Files

The StreamReader and StreamWriter classes are used for reading from and writing data to text files. These classes inherit from the abstract base class Stream, which supports reading and writing bytes into a file stream.


The StreamReader Class

The StreamReader class also inherits from the abstract base class TextReader that represents a reader for reading series of characters. The following table describes some of the commonly used methods of the StreamReader class:

  +----+---------------------------------------------------------------+
  | S.N| Method Name & Purpose                                         |
  +----+---------------------------------------------------------------+
  | 1  | public override void Close()                                  |
  |    |                                                               |
  |    | It closes the StreamReader object and the underlying stream,  |
  |    | and releases any system resources associated with the reader. |
  +----+---------------------------------------------------------------+
  |  2 |  public override int Peek()                                   |
  |    |                                                               |
  |    |  Returns the next available character but does not consume it.|
  +----+---------------------------------------------------------------+
  | 3  | public override int Read()                                    |
  |    |                                                               |
  |    | Reads the next character from the input stream and advances   |
  |    | the character position by one character.                      |
  +----+---------------------------------------------------------------+

Example:

The following example demonstrates reading a text file named Jamaica.txt. The file reads:

  Down the way where the nights are gay
  And the sun shines daily on the mountain top
  I took a trip on a sailing ship
  And when I reached Jamaica
  I made a stop

  using System;
  using System.IO;

  namespace FileApplication
  {
      class Program
      {
          static void Main(string[] args)
          {
              try
              {
                  // Create an instance of StreamReader to read from a file. 
                  // The using statement also closes the StreamReader. 
                  using (StreamReader sr = new StreamReader("c:/jamaica.txt"))
                  {
                      string line;
                     
                      // Read and display lines from the file until 
                      // the end of the file is reached. 
                      while ((line = sr.ReadLine()) != null)
                      {
                          Console.WriteLine(line);
                      }
                  }
              }
              catch (Exception e)
              {
                  // Let the user know what went wrong.
                  Console.WriteLine("The file could not be read:");
                  Console.WriteLine(e.Message);
              }
              Console.ReadKey();
          }
      }
  }

Guess what it displays when you compile and run the program!


The StreamWriter Class

The StreamWriter class inherits from the abstract class TextWriter that represents a writer, which can write a series of character.

The following table shows some of the most commonly used methods of this class:

  +----+---------------------------------------------------------------+
  | S.N| Method Name & Purpose                                         |
  +----+---------------------------------------------------------------+
  | 1  | public override void Close()                                  |
  |    |                                                               |
  |    | Closes the current StreamWriter object and the underlying     |
  |    | stream.                                                       |
  +----+---------------------------------------------------------------+
  | 2  | public override void Flush()                                  |
  |    |                                                               |
  |    | Clears all buffers for the current writer and causes any      |
  |    | buffered data to be written to the underlying stream.         |
  +----+---------------------------------------------------------------+
  | 3  | public virtual void Write(bool value)                         |
  |    |                                                               |
  |    | Writes the text representation of a Boolean value to the text |
  |    | string or stream. (Inherited from TextWriter.)                |
  +----+---------------------------------------------------------------+
  | 4  | public override void Write( char value )                      |
  |    |                                                               |
  |    | Writes a character to the stream.                             |
  +----+---------------------------------------------------------------+
  | 5  | public virtual void Write( decimal value )                    |
  |    |                                                               |
  |    | Writes the text representation of a decimal value to the text |
  |    | string or stream.                                             |
  +----+---------------------------------------------------------------+
  | 6  | public virtual void Write( double value )                     |
  |    |                                                               |
  |    | Writes the text representation of an 8-byte floating-point    |
  |    | value to the text string or stream.                           |
  +----+---------------------------------------------------------------+
  | 7  | public virtual void Write( int value )                        |
  |    |                                                               |
  |    | Writes the text representation of a 4-byte signed integer to  |
  |    | the text string or stream.                                    |
  +----+---------------------------------------------------------------+
  | 8  | public override void Write( string value )                    |
  |    |                                                               |
  |    | Writes a string to the stream.                                |
  +----+---------------------------------------------------------------+
  | 9  | public virtual void WriteLine()                               |
  |    |                                                               |
  |    | Writes a line terminator to the text string or stream.        |
  +----+---------------------------------------------------------------+

For complete list of methods, please visit Microsoft's C# documentation.

Example:

The following example demonstrates writing text data into a file using the StreamWriter class:

  using System;
  using System.IO;

  namespace FileApplication
  {
      class Program
      {
          static void Main(string[] args)
          {

              string[] names = new string[] {"Zara Ali", "Nuha Ali"};
              using (StreamWriter sw = new StreamWriter("names.txt"))
              {
                  foreach (string s in names)
                  {
                      sw.WriteLine(s);

                  }
              }

              // Read and show each line from the file. 
              string line = "";
              using (StreamReader sr = new StreamReader("names.txt"))
              {
                  while ((line = sr.ReadLine()) != null)
                  {
                      Console.WriteLine(line);
                  }
              }
              Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Zara Ali
  Nuha Ali

----------

C# - Reading from and Writing into Binary files

The BinaryReader and BinaryWriter classes are used for reading from and writing to a binary file.
The BinaryReader Class

The BinaryReader class is used to read binary data from a file. A BinaryReader object is created by passing a FileStream object to its constructor.

The following table shows some of the commonly used methods of the BinaryReader class.

  +-----+--------------------------------------------------------------+
  | S.N | Method Name & Purpose                                        |
  +-----+--------------------------------------------------------------+
  | 1   | public override void Close()                                 |
  |     |                                                              |
  |     | It closes the BinaryReader object and the underlying stream. |
  +-----+--------------------------------------------------------------+
  | 2   | public virtual int Read()                                    |
  |     |                                                              |
  |     | Reads the characters from the underlying stream and advances |
  |     | the current position of the stream.                          |
  +-----+--------------------------------------------------------------+
  | 3   | public virtual bool ReadBoolean()                            |
  |     |                                                              |
  |     | Reads a Boolean value from the current stream and advances   |
  |     | the current position of the stream by one byte.              |
  +-----+--------------------------------------------------------------+
  | 4   | public virtual byte ReadByte()                               |
  |     |                                                              |
  |     | Reads the next byte from the current stream and advances the |
  |     | current position of the stream by one byte.                  |
  +-----+--------------------------------------------------------------+
  | 5   | public virtual byte[] ReadBytes( int count )                 |
  |     |                                                              |
  |     | Reads the specified number of bytes from the current stream  |
  |     | into a byte array and advances the current position by that  |
  |     | number of bytes.                                             |
  +-----+--------------------------------------------------------------+
  | 6   | public virtual char ReadChar()                               |
  |     |                                                              |
  |     | Reads the next character from the current stream and         |
  |     | advances the current position of the stream in accordance    |
  |     | with the Encoding used and the specific character being read |
  |     | from the stream.                                             |
  +-----+--------------------------------------------------------------+
  | 7   | public virtual char[] ReadChars( int count )                 |
  |     |                                                              |
  |     | Reads the specified number of characters from the current    |
  |     | stream, returns the data in a character array, and advances  |
  |     | the current position in accordance with the Encoding used    |
  |     | and the specific character being read from the stream.       |
  +-----+--------------------------------------------------------------+
  | 8   | public virtual double ReadDouble()                           |
  |     |                                                              |
  |     | Reads an 8-byte floating point value from the current stream |
  |     | and advances the current position of the stream by eight     |
  |     | bytes.                                                       |
  +-----+--------------------------------------------------------------+
  | 9   | public virtual int ReadInt32()                               |
  |     |                                                              |
  |     | Reads a 4-byte signed integer from the current stream and    |
  |     | advances the current position of the stream by four bytes.   |
  +-----+--------------------------------------------------------------+
  | 10  | public virtual string ReadString()                           |
  |     |                                                              |
  |     | Reads a string from the current stream. The string is        |
  |     | prefixed with the length, encoded as an integer seven bits   |
  |     | at a time.                                                   |
  +-----+--------------------------------------------------------------+


The BinaryWriter Class

The BinaryWriter class is used to write binary data to a stream. A BinaryWriter object is created by passing a FileStream object to its constructor.

The following table shows some of the commonly used methods of the BinaryWriter class.

  +-----+--------------------------------------------------------------+
  | S.N | Function Name & Description                                  |
  +-----+--------------------------------------------------------------+
  | 1   | public override void Close()                                 |
  |     |                                                              |
  |     | It closes the BinaryWriter object and the underlying stream. |
  +-----+--------------------------------------------------------------+
  | 2   | public virtual void Flush()                                  |
  |     |                                                              |
  |     | Clears all buffers for the current writer and causes any     |
  |     | buffered data to be written to the underlying device.        |
  +-----+--------------------------------------------------------------+
  | 3   | public virtual long Seek( int offset, SeekOrigin origin )    |
  |     |                                                              |
  |     | Sets the position within the current stream.                 |
  +-----+--------------------------------------------------------------+
  | 4   | public virtual void Write( bool value )                      |
  |     |                                                              |
  |     | Writes a one-byte Boolean value to the current stream,       |
  |     | with 0 representing false and 1 representing true.           |
  +-----+--------------------------------------------------------------+
  | 5   | public virtual void Write( byte value )                      |
  |     |                                                              |
  |     | Writes an unsigned byte to the current stream and advances   |
  |     | the stream position by one byte.                             |
  +-----+--------------------------------------------------------------+
  | 6   | public virtual void Write( byte[] buffer )                   |
  |     |                                                              |
  |     | Writes a byte array to the underlying stream.                |
  +-----+--------------------------------------------------------------+
  | 7   | public virtual void Write( char ch )                         |
  |     |                                                              |
  |     | Writes a Unicode character to the current stream and         |
  |     | advances the current position of the stream in accordance    |
  |     | with the Encoding used and the specific characters being     |
  |     | written to the stream.                                       |
  +-----+--------------------------------------------------------------+
  | 8   | public virtual void Write( char[] chars )                    |
  |     |                                                              |
  |     | Writes a character array to the current stream and           |
  |     | advances the current position of the stream in accordance    |
  |     | with the Encoding used and the specific characters being     |
  |     | written to the stream.                                       |
  +-----+--------------------------------------------------------------+
  | 9   | public virtual void Write( double value )                    |
  |     |                                                              |
  |     | Writes an eight-byte floating-point value to the current     |
  |     | stream and advances the stream position by eight bytes.      |
  +-----+--------------------------------------------------------------+
  | 10  | public virtual void Write( int value )                       |
  |     |                                                              |
  |     | Writes a four-byte signed integer to the current stream      |
  |     | and advances the stream position by four bytes.              |
  +-----+--------------------------------------------------------------+
  | 11  | public virtual void Write( string value )                    |
  |     |                                                              |
  |     | Writes a length-prefixed string to this stream in the        |
  |     | current encoding of the BinaryWriter, and advances the       |
  |     | current position of the stream in accordance with the        |
  |     | encoding used and the specific characters being written to   |
  |     | the stream.                                                  |
  +-----+--------------------------------------------------------------+

For complete list of methods, please visit Microsoft's C# documentation.

Example

The following example demonstrates reading and writing binary data:

  using System;
  using System.IO;

  namespace BinaryFileApplication
  {
      class Program
      {
          static void Main(string[] args)
          {
              BinaryWriter bw;
              BinaryReader br;
              int i = 25;
              double d = 3.14157;
              bool b = true;
              string s = "I am happy";
              //create the file
              try
              {
                  bw = new BinaryWriter(new FileStream("mydata",
                                        FileMode.Create));
              }
              catch (IOException e)
              {
                  Console.WriteLine(e.Message + "\n Cannot create file.");
                  return;
              }
              //writing into the file
              try
              {
                  bw.Write(i);
                  bw.Write(d);
                  bw.Write(b);
                  bw.Write(s);
              }
              catch (IOException e)
              {
                  Console.WriteLine(e.Message + "\n Cannot write to file.");
                  return;
              }

              bw.Close();
              //reading from the file
              try
              {
                  br = new BinaryReader(new FileStream("mydata",
                                        FileMode.Open));
              }
              catch (IOException e)
              {
                  Console.WriteLine(e.Message + "\n Cannot open file.");
                  return;
              }
              try
              {
                  i = br.ReadInt32();
                  Console.WriteLine("Integer data: {0}", i);
                  d = br.ReadDouble();
                  Console.WriteLine("Double data: {0}", d);
                  b = br.ReadBoolean();
                  Console.WriteLine("Boolean data: {0}", b);
                  s = br.ReadString();
                  Console.WriteLine("String data: {0}", s);
              }
              catch (IOException e)
              {
                  Console.WriteLine(e.Message + "\n Cannot read from file.");
                  return;
              }
              br.Close();
              Console.ReadKey();
          }
      }
  }

When the above code is compiled and executed, it produces the following result:

  Integer data: 25
  Double data: 3.14157
  Boolean data: True
  String data: I am happy

----------

C# - Windows File System

C# allows you to work with the directories and files using various directory and file related classes like, the DirectoryInfo class and the FileInfo class.
The DirectoryInfo Class

The DirectoryInfo class is derived from the FileSystemInfo class. It has various methods for creating, moving, and browsing through directories and subdirectories. This class cannot be inherited.

Following are some commonly used properties of the DirectoryInfo class:

  +-----+--------------------------------------------------------------+
  | S.N | Property Name & Description                                  |
  +-----+--------------------------------------------------------------+
  | 1   | Attributes                                                   |
  |     |                                                              |
  |     | Gets the attributes for the current file or directory.       |
  +-----+--------------------------------------------------------------+
  | 2   | CreationTime                                                 |
  |     |                                                              |
  |     | Gets the creation time of the current file or directory.     |
  +-----+--------------------------------------------------------------+
  | 3   | Exists                                                       |
  |     |                                                              |
  |     | Gets a Boolean value indicating whether the directory        |
  |     | exists.                                                      |
  +-----+--------------------------------------------------------------+
  | 4   | Extension                                                    |
  |     |                                                              |
  |     | Gets the string representing the file extension.             |
  +-----+--------------------------------------------------------------+
  | 5   | FullName                                                     |
  |     |                                                              |
  |     | Gets the full path of the directory or file.                 |
  +-----+--------------------------------------------------------------+
  | 6   | LastAccessTime                                               |
  |     |                                                              |
  |     | Gets the time the current file or directory was last         |
  |     | accessed.                                                    |
  +-----+--------------------------------------------------------------+
  | 7   | Name                                                         |
  |     |                                                              |
  |     | Gets the name of this DirectoryInfo instance.                |
  +-----+--------------------------------------------------------------+

Following are some commonly used methods of the DirectoryInfo class:

  +-----+--------------------------------------------------------------+
  | S.N | Method Name & Purpose                                        |
  +-----+--------------------------------------------------------------+
  | 1   | public void Create()                                         |
  |     |                                                              |
  |     | Creates a directory.                                         |
  +-----+--------------------------------------------------------------+
  | 2   | public DirectoryInfo CreateSubdirectory( string path )       |
  |     |                                                              |
  |     | Creates a subdirectory or subdirectories on the specified    |
  |     | path. The specified path can be relative to this instance    |
  |     | of the DirectoryInfo class.                                  |
  +-----+--------------------------------------------------------------+
  | 3   | public override void Delete()                                |
  |     |                                                              |
  |     | Deletes this DirectoryInfo if it is empty.                   |
  +-----+--------------------------------------------------------------+
  | 4   | public DirectoryInfo[] GetDirectories()                      |
  |     |                                                              |
  |     | Returns the subdirectories of the current directory.         |
  +-----+--------------------------------------------------------------+
  | 5   | public FileInfo[] GetFiles()                                 |
  |     |                                                              |
  |     | Returns a file list from the current directory.              |
  +-----+--------------------------------------------------------------+

For complete list of properties and methods please visit Microsoft's C# documentation.
The FileInfo Class

The FileInfo class is derived from the FileSystemInfo class. It has properties and instance methods for creating, copying, deleting, moving, and opening of files, and helps in the creation of FileStream objects. This class cannot be inherited.

Following are some commonly used properties of the FileInfo class:

  +-----+--------------------------------------------------------------+
  | S.N | Property Name & Description                                  |
  +-----+--------------------------------------------------------------+
  | 1   | Attributes                                                   |
  |     |                                                              |
  |     | Gets the attributes for the current file.                    |
  +-----+--------------------------------------------------------------+
  | 2   | CreationTime                                                 |
  |     |                                                              |
  |     | Gets the creation time of the current file.                  |
  +-----+--------------------------------------------------------------+
  | 3   | Directory                                                    |
  |     |                                                              |
  |     | Gets an instance of the directory which the file belongs to. |
  +-----+--------------------------------------------------------------+
  | 4   | Exists                                                       |
  |     |                                                              |
  |     | Gets a Boolean value indicating whether the file exists.     |
  +-----+--------------------------------------------------------------+
  | 5   | Extension                                                    |
  |     |                                                              |
  |     | Gets the string representing the file extension.             |
  +-----+--------------------------------------------------------------+
  | 6   | FullName                                                     |
  |     |                                                              |
  |     | Gets the full path of the file.                              |
  +-----+--------------------------------------------------------------+
  | 7   | LastAccessTime                                               |
  |     |                                                              |
  |     | Gets the time the current file was last accessed.            |
  +-----+--------------------------------------------------------------+
  | 8   | LastWriteTime                                                |
  |     |                                                              |
  |     | Gets the time of the last written activity of the file.      |
  +-----+--------------------------------------------------------------+
  | 9   | Length                                                       |
  |     |                                                              |
  |     | Gets the size, in bytes, of the current file.                |
  +-----+--------------------------------------------------------------+
  | 10  | Name                                                         |
  |     |                                                              |
  |     | Gets the name of the file.                                   |
  +-----+--------------------------------------------------------------+

Following are some commonly used methods of the FileInfo class:

  +-----+--------------------------------------------------------------+
  | S.N | Method Name & Purpose                                        |
  +-----+--------------------------------------------------------------+
  | 1   | public StreamWriter AppendText()                             |
  |     |                                                              |
  |     | Creates a StreamWriter that appends text to the file         |
  |     | represented by this instance of the FileInfo.                |
  +-----+--------------------------------------------------------------+
  | 2   | public FileStream Create()                                   |
  |     |                                                              |
  |     | Creates a file.                                              |
  +-----+--------------------------------------------------------------+
  | 3   | public override void Delete()                                |
  |     |                                                              |
  |     | Deletes a file permanently.                                  |
  +-----+--------------------------------------------------------------+
  | 4   | public void MoveTo( string destFileName )                    |
  |     |                                                              |
  |     | Moves a specified file to a new location, providing the      |
  |     | option to specify a new file name.                           |
  +-----+--------------------------------------------------------------+
  | 5   | public FileStream Open( FileMode mode )                      |
  |     |                                                              |
  |     | Opens a file in the specified mode.                          |
  +-----+--------------------------------------------------------------+
  | 6   | public FileStream Open( FileMode mode, FileAccess access )   |
  |     |                                                              |
  |     | Opens a file in the specified mode with read, write,         |
  |     | or read/write access.                                        |
  +-----+--------------------------------------------------------------+
  | 7   | public FileStream Open(                                      |
  |     |     FileMode mode,                                           |
  |     |     FileAccess access,                                       |
  |     |     FileShare share                                          |
  |     | )                                                            |
  |     |                                                              |
  |     | Opens a file in the specified mode with read, write, or      |
  |     | read/write access and the specified sharing option.          |
  +-----+--------------------------------------------------------------+
  | 8   | public FileStream OpenRead()                                 |
  |     |                                                              |
  |     | Creates a read-only FileStream                               |
  +-----+--------------------------------------------------------------+
  | 9   | public FileStream OpenWrite()                                |
  |     |                                                              |
  |     | Creates a write-only FileStream.                             |
  +-----+--------------------------------------------------------------+

For complete list of properties and methods, please visit Microsoft's C# documentation

Example

The following example demonstrates the use of the above-mentioned classes:

  using System;
  using System.IO;

  namespace WindowsFileApplication
  {
      class Program
      {
          static void Main(string[] args)
          {
              //creating a DirectoryInfo object
              DirectoryInfo mydir = new DirectoryInfo(@"c:\Windows");

              // getting the files in the directory, their names and size
              FileInfo [] f = mydir.GetFiles();
              foreach (FileInfo file in f)
              {
                  Console.WriteLine("File Name: {0} Size: {1}",
                                    file.Name, file.Length);
              }
              Console.ReadKey();
          }
      }
  }

When you compile and run the program, it displays the names of files and their size in the Windows directory.
