Reverse word of full sentence

You would need to split the string into words and the reverse those instead of reversing the characters:

text = String.Join(" ", text.Split(' ').Reverse())

In framework 3.5:

text = String.Join(" ", text.Split(' ').Reverse().ToArray())

In framework 2.0:

string[] words = text.Split(' ');
Array.Reverse(words);
text = String.Join(" ", words);

"please send me the code of this program."

Okay ...

using System;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        string text = "My name is Archit Patel";

        Console.WriteLine(string.Join(" ", text.Split(' ').Reverse()));
    }
}

Now: what have you learned?

Also, as Guffa points out, for versions below .Net 4.0 you'll need to add .ToArray() since string.Join doesn't have the correct overload in those versions.