static void Main(string[] args)
        {

            Console.WriteLine("Press 1 or 2 to select your choice");
            Console.WriteLine("1. Display all didigts from 9 to 0 using a for loop");
            Console.WriteLine("2. Display all didigts from 9 to 0 using a while loop");
            string choice = Console.ReadLine();

            if (choice == "1")
            {
                for (int i = 9; i >= 0; i--)
                {
                    Console.WriteLine(i);
                }
            }
            else if (choice == "2")
            {
                int j = 9;
                while (j >= 0)
                {
                    Console.WriteLine(j);
                    j--;
                }
            }
            else
                return;


            Console.ReadKey();

        }