C# Basics

C# is a modern, general-purpose, object-oriented programming language developed by Microsoft and approved by European Computer Manufacturers Association (ECMA) and International Standards Organization (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 on different computer platforms and architectures.

Programming Features of C#

Although C# constructs closely follow traditional high-level languages, C and C++ and being an object-oriented programming language. 

 Important features of C#:

• 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

 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 consists of an enormous library of codes used by the client languages such as 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

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

C# - Program Structure

Before we study basic building blocks of the C# programming language, let us look at a bare minimum C# program structure

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 a simple code that prints the words "Hello World"

Output

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 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 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.

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# - Basic Syntax

1. 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.

2. The class Keyword

                 The class keyword is used for declaring a class.

3. 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.

4. 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.

5. 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.

6. Instantiating a Class

                 In the preceding program, the class ExecuteRectangle contains the Main()
                 method and instantiates the Rectangle class.

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

C# - Data Types

C# is a strongly typed language. It means, that you cannot use variable without data types. Data types tell the compiler that which type of data is used for processing. 
Such as if you want to work with string value then you will have to assign string type variable to work with. 

C# provides two types of data types: 

1.Value types 
2.Reference types.


A Value type data type stores copy of the value whereas the Reference type data types stores the address of the value.

Value Types 

Data Types	Size	Values
sbyte	8 bit	-128 to 127
byte	8 bit	0 to 255
short	16 bit	-32,768 to 32,767
ushort	16 bit	0 to 65,535
int	32 bit	-2,147,483,648 to 2,147,483,647
uint	32 bit	0 to 4,294,967,295
long	64 bit	-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
ulong	64 bit	0 to 18,446,744,073,709,551,615
char	16 bit	0 to 65535
float	32 bit	-1.5 x 1045 to 3.4 x 1038
double	64 bit	-5 x 10324 to 1.7 x 10308
decimal	128 bit	-1028 to 7.9 x 1028

Reference Types

Data Types	Size	Values
string	Variable length	0-2 billion Unicode characters
object	---	---

C# - Varables 

A variable is nothing but a name given to a storage area that our programs can manipulate.

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

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;

The following example uses various types of variables:

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

C# -Conditional Statements

This statement allows you to branch your code depending on whether or not a certain condition is met.

In C# are the following 2 conditional branching statements:

1. IF statement
2. Switch statement

IF Statement

The if statement allows you to test whether or not a specific condition is met.

Syntax

If(<Condition>) 

<statements>; 

Else if(<Condition>) 

<statements>; 

--------------------- 

----------------------- 

Else 

<statements>; 

Example

W.A.P to find the greatest number using an if statement:

Switch Statement

The switch statement compares two logical expressions.

Syntax

Switch(<Expression>) 

{ 

Case <Value> : 

<stmts> 

Break; 

----------------------- 

------------------------- 

------------------------ 

Default : 

<stmts> 

Break; 

}

Foreach Loop

It is specially designed for accessing the values of an array and collection.

Syntax

1. Foreach(type var in coll/Arr)  
2. {  
3. < statement >;  
4. }  

C# - Loop 

There may be a situation, when you need to execute a block of code several number of times. In general, the 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.

C# provides following types of loop to handle looping requirements. Click the following links to check their detail.

Loop Type	Description
while loop	It repeats a statement or a group of statements while a given condition is true. It tests the condition before executing the loop body.
for loop	It executes a sequence of statements multiple times and abbreviates the code that manages the loop variable.
do...while loop	It is similar to 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 doWhile loop.

C# - Arrays

An array stores a fixed-size sequential collection of elements of the same type.

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

Declaring Arrays

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

datatype[ ] arrayName;

For example,

int [ ] array =new int[4];

string [ ] array =new string [10];

double[ ] balance;

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.

1. Try: A try block identifies a block of code for which particular exceptions is activated. It is followed by one or more catch blocks.

2. 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.

3. 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.

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

Author : Sandeep Kumar Jha

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