Checking .Net frameworks is installed or not on local machine by C#

• Environment.Version property of .Net framework. For example, this simple C# source code can be compiled to a .Net console program that shows .Net framework version installed:

  using System;
  
  class Version
  {
    public static void Main()
    {
      Console.WriteLine();
      Console.WriteLine(".Net Framework Version {0}",
         Environment.Version.ToString());
    }
  }

  
  You don't have to install Visual Studio except the .Net framework SDK (which package all the .Net command line compilers, including the C# compiler). Thus, to compile the C# code in a source file called sample.cs with C# command line compiler, just enter this at Command Prompt:
  
  csc sample.cs
• Limitation of Environment.Version property – only one of the multiple .Net framework versions installed will be reported. I.e. if you've .Net 2.0, .Net 3.0 and .Net 3.5 version installed, Environment.Version reports only .Net 2.0 framework.
  To overcome this problem, Aaron Stebner's .Net version checker source code is better choice, where the programming approach is to query the Windows Registry keys and also call the mscoree.dll exported APIs to report the presence of all .NET Framework versions.

http://www.vcskicks.com/detect_net_framework.php