The String object is immutable.
A string requires a new allocation of space for every new object.
In situations where you need to perform repeated modifications to a string,a new String object can be costly.
The System.Text.StringBuilder class can be used when you want to modify a string without creating a new object.

using System;
using System.Text;

namespace forgetCode
{    
    class program
    {        
        public static void Main()
        {
            StringBuilder sb = new StringBuilder();            

            sb.AppendLine("Forget Code");
            sb.AppendLine("works");
            sb.AppendLine("nicely");

            Console.Write(sb.ToString());                      
        }
    }
}

Output:

Forget Code
works
nicely