• Start Visual Studio  and select File -- New project  
• From the project dialog, select the Console application 
• In the Console Application in Program.cs  File write the below program to reverse a string in (c#)csharp .net 
• In this reverse string program in csharp we are taking a string as user input
• After taking the user input string we are looping using for loop for string.length times and appending the reverse string to a string variable and finally we are displaying the output 
• you can refer below program for code and with live demo and output

 using System;

 namespace ReverseSample
 {
            class StringReverse
            {
                public static void Main()
                {

                    string Str, Revstr = ""; 
                    Console.Write("Enter A String : ");
                    Str = Console.ReadLine();

                    for (int i = Str.Length - 1; i >= 0; i--)
                    {

                        Revstr = Revstr + Str[i];
                    }

                    Console.WriteLine("Reverse  String  Is  {0}", Revstr);
                    Console.ReadLine();
                }
           }
   }