Lesson 2: Program Structure And Basic Syntax


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.

Creating Hello World Program

A C# program consists of the following parts:

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

Let us look at implementation of a Rectangle class and discuss C# basic syntax:

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:

Hello World

Let us look at the various parts of the given 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 usingstatements.

  • 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 contain multiple methods. 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 does when executed.

  • The next line /*...*/ is ignored by the compiler and it is put to add comments in the program.

  • The Main method specifies its behavior with the statementConsole.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 is 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, program file name could be different from the class name.

Compiling and Executing the 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 click OK button.

  • This creates a new project in Solution Explorer.

  • Write code in the Code Editor.

  • Click the Run button or press F5 key to execute 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 takes you to the next line and generates helloworld.exe executable file.

  • Type helloworld to execute your program.

  • You can see the output 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, are said to be in the same class.

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

Let us look at implementation of a Rectangle class and discuss C# basic syntax:

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 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 such as? - + ! @ # % ^ & * ( ) [ ] { } . ; : " ' / 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 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    

 

Source: tutorialspoint


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