A do while loop is similar to the while loop, except that it checks its condition at the end of the loop. This means that the do loop is guaranteed to execute at least one time.

One reason you may want to use a do loop instead of a while loop is to present a message or menu.
The Do Loop: DoLoop.cs

using System;
class DoLoop
{
   public static void Main()
    {
        string myChoice;

        do
       {
            // Print A Menu
            Console.WriteLine("My Address Book\n");

            Console.WriteLine("A - Add New Address");
            Console.WriteLine("D - Delete Address");
            Console.WriteLine("M - Modify Address");
            Console.WriteLine("V - View Addresses");
            Console.WriteLine("Q - Quit\n");

            Console.WriteLine("Choice (A,D,M,V,or Q): ");

            // Retrieve the user's choice
            myChoice = Console.ReadLine();

            // Make a decision based on the user's choice
            switch(myChoice)
            {
                case "A":
                case "a":
                    Console.WriteLine("You wish to add an address.");
                    break;
                case "D":
                case "d":
                    Console.WriteLine("You wish to delete an address.");
                    break;
                case "M":
                case "m":
                    Console.WriteLine("You wish to modify an address.");
                    break;
                case "V":
                case "v":
                    Console.WriteLine("You wish to view the address list.");
                    break;
                case "Q":
                case "q":
                    Console.WriteLine("Bye.");
                    break;
                default:
                    Console.WriteLine("{0} is not a valid choice", myChoice);
                    break;
            }

            // Pause to allow the user to see the results
            Console.Write("press Enter key to continue...");
            Console.ReadLine();
            Console.WriteLine();
        } while (myChoice != "Q" && myChoice != "q"); // Keep going until the user wants to quit
   }
}