Learn C# programming - Program Structure & Basic Syntax

Learn C# Programming
Program Structure & Basic Syntax
Eng Teong Cheah
Microsoft MVP in Visual Studio &
Development Technologies

Agenda
•Program Structure
•Basic Syntax

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.

Create 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 a simple code that prints the words “Hello World”:
When this 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 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 contain multiple methods. Methods define the behaviour
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 specified its behaviour 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 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.

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, are said to be in the same class.

C# - Basic Syntax
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.
Lets us look at implementation of a Rectangle and discuss
C# basic syntax:

C# - Basic Syntax
Length: 4.5
Width: 3.5
Area: 15.75
When the code is compiled and
executed, it produces the
following result:

C# - Basic Syntax
The using Keyword
The first statement in any C# program is
using System;
The using keyword is used for including the
namespace in the program. A program can include
multiple using statements.

C# - Basic Syntax
The class Keyword
The class keyword is used for declaring a class.

C# - Basic Syntax
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.

C# - Basic Syntax
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.

C# - Basic Syntax
Instantiating a Class
In the preceding program, the class ExecuteRectangle
contains the Main() method and instantiates the
Rectangle class.

C# - Basic Syntax
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.

C# - Basic Syntax
Identifiers
-It must not contain any embedded space or symbol such as ? -
+ ! @ # % ^ & * ( ) [ ] { } . ; : “ ‘ / and . However, an underscore
(_) can be used.

C# - Basic Syntax
Identifiers
- It should not be a C# keyword.

C# - Basic Syntax
C# Keywords
Keywords are reserved words predefined to the C# compiler.
Theses 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.

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

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

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