Introduction

WHAT IS THE .NET FRAMEWORK?

The .NET Framework  is a revolutionary platform created by Microsoft for developing applications.
Although the Microsoft release of the .NET Framework runs on the Windows operating system, it is possible to find alternative versions that will work on other systems. One example of this is Mono, an open-source version of the .NET Framework (including a C# compiler) that runs on several operating systems, including various flavors of Linux and Mac OS. In addition, you can use the Microsoft .NET Compact Framework (essentially a subset of the full .NET Framework) on personal digital assistant (PDA) class devices and even some smartphones. One of the key motivations behind the .NET Framework is its intended use as a means of integrating disparate operating systems.
The .NET Framework enables the creation of Windows applications, Web applications, Web services, and pretty much anything else you can think of.
The .NET Framework has been designed so that it can be used from any language, including C# as well as C++, Visual Basic, JScript, and even older languages such as COBOL.

What’s in the .NET Framework?

Writing an application using the .NET Framework means writing code (using any of the languages that support the Framework) using the .NET code library.

The .NET Framework consists primarily of a gigantic library of code that you use from your client languages (such as C#) using object-oriented programming (OOP) techniques. This library is categorized into different modules — you use portions of it depending on the results you want to achieve.

The .Net Framework includes the .NET Common Language Runtime (CLR), which is responsible for maintaining the execution of all applications developed using the .NET library.

CIL and JIT

Compile code that uses the .NET Framework library, you don’t immediately create operating-system-specific native code. Instead, you compile your code into Common Intermediate Language (CIL) code. This code isn’t specific to any operating system (OS) and isn’t specific to C#.
Obviously, more work is necessary to execute an application. That is the job of a just-in-time (JIT) compiler, which compiles CIL into native code that is specific to the OS and machine architecture being targeted.

NOTE: You may come across references to Microsoft Intermediate Language (MSIL) or just IL. MSIL was the original name for CIL, and many developers still use this terminology.

Assemblies

When you compile an application, the CIL code created is stored in an assembly. Assemblies include both executable application files that you can run directly from Windows without the need for any other programs (these have a .exe file extension) and libraries (which have a .dll extension) for use by other applications.
In addition to containing CIL, assemblies also include metadata (that is, information about the information contained in the assembly) and optional resources (additional data used by the CIL, such as sound files and pictures).

Managed Code

Code written using the .NET Framework is managed when it is executed (a stage usually referred to as runtime). This means that the CLR looks after your applications by managing memory, handling security, allowing cross-language debugging, and so on.

Garbage Collection

One of the most important features of managed code is the concept of garbage collection. This is the .NET method of making sure that the memory used by an application is freed up completely when the application is no longer in use.

Applications You Can Write with C#

• Windows applications
• Web applications
• Web services

Any of these types may also require some form of database access, which can be achieved using the ADO.NET (Active Data Objects .NET) section of the .NET Framework, or through the LINQ (Language Integrated Query) capabilities of C#. Many other resources can be drawn on, such as tools for creating networking components, outputting graphics, performing complex mathematical tasks, and so on.

Writing a C# Program

If this is the first time you have to use Visual Studio don't panic, you can download an " Express version " for free.  

Visual Studio Express

http://www.visualstudio.com/en-us/downloads#d-2012-express

Microsoft Visual Studio Express 2013 for Web

Visual Studio Express 2013 for Web provides the core tools for creating compelling, innovative web applications and services.

Microsoft Visual Studio Express 2013 for Windows

Visual Studio Express 2013 for Windows provides the core tools that are required to build compelling, innovative Windows Store apps.

Microsoft Visual Studio Express 2013 for Windows Desktop

Visual Studio Express 2013 for Windows Desktop enables the creation of desktop apps in C#, Visual Basic, and C++, and supports Windows Presentation Foundation (WPF), Windows Forms, and Win32.

Microsoft Visual Studio Team Foundation Server Express 2013

Visual Studio Team Foundation Server Express 2013 is a source-code-control, project-management, and team-collaboration platform at the core of the Microsoft suite of Application Lifecycle Management (ALM) tools, which help individuals and small teams be more agile, collaborate more effectively, and deliver quality software more consistently.

The first application you create is a simple console application. Console applications are those that don’t make use of the graphical windows environment, so you won’t have to worry about buttons, menus, interaction with the mouse pointer, and so on. Instead, you run the application in a command prompt window and interact with it in a much simpler way.

The second application is a Windows Forms application. The look and feel of this is very familiar to Windows users, and (surprisingly) the application doesn’t require much more effort to create.

Microsoft Visual Studio Express 2013 for Windows Desktop will be more than enough in the first stage.

Install Instructions

Choose one of these installation options:

• To install over the Internet:

• On this page, choose the Download button.

• Select the .exe option and then choose the Next button.

• To install now, choose the Run button.

• To download an installer that you can run later, choose the Save button. (When you install, the computer must be connected to the Internet.)

• To download an image to burn on a DVD:

• On this page, choose the Download button.

• Select the .iso option and then choose the Next button.

• Choose the Save button to download a DVD5 ISO image so that you can burn a DVD later.