C# First Program

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 Systemnamespace in the program. A program generally has multiple using statements.
• The next line has the namespace declaration. A namespace is a collection of classes. TheHelloWorldApplication 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 methodMain.
• The next line defines the Main method, which is the entry point for all C# programs. The Mainmethod states what the class will do when executed
• The next line /*...*/ will be ignored by the compiler and it has been put to add additionalcomments 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# 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, theRectangle 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 (generic modifier)	int
interface	internal	is	lock	long	namespace	new
null	object	operator	out	out (generic modifier)	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
Contextual Keywords
add	alias	ascending	descending	dynamic	from	get
global	group	into	join	let	orderby	partial (type)
partial (method)	remove	select	set