code

using System;

    class Program
    {
        static void Main()
        {
            int totalprice = 0;
            start:
            Console.WriteLine("select coffie 1 =small, 2= normal 3=large");
          int usernum =int.Parse(Console.ReadLine());
            switch (usernum)
            { 
                case 1:

                    totalprice += 1;
                   
                    break;
                case 2:

                    totalprice += 2;
                  
                    break;
                case 3:

                    totalprice += 3;
                  
                    break;
                default:
                    Console.WriteLine("invalid selection");
                    Console.ReadLine();
                   goto start;

            }
            decide:
            Console.WriteLine("you need another cup? yes or no");
            String xxx = Console.ReadLine();
            switch (xxx)
            { 
                case "yes":
                    goto start;
                case "no":
                    break;
                default:
                    Console.WriteLine("invalid selection");
                    goto decide;

            }
            Console.WriteLine("total bill = {0}", totalprice * 100);
            Console.ReadLine();
        }
    }