קוד רקורסיה

using System;

namespace ConsoleApp12
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = 7;
            int f = factorial(n);

            Console.WriteLine("* * * * * * * f a c t o r i a l * * * * * * *");
            Console.WriteLine("final result: factorial({0}) = {1}", n, f);

            int x = 3219786;
            int d = 2;

            Console.WriteLine("\n\n* * * * * * * * h a s * * * * * * * *");
            if (has(x, d))
                Console.WriteLine("{0} has a digit equals to {1}", x, d);
            else
                Console.WriteLine("{0} does not have a digit equals to {1}", x, d);
        }

        public static bool has(int n, int k)
        {
            Console.WriteLine("start searching in {0} for {1}", n, k);
            if (n == 0)
            {
                Console.WriteLine("stop searching. {0} was not found", k);
                return false;
            }

            int a = n % 10;   // ahad only
            int rest = n / 10; // number without ahad

            if (k == a)
            {
                Console.WriteLine("{0} starts with the digit {1}", n, k);
                return true;
            }

            return has(rest, k);
        }

        public static int factorial(int n)
        {
            Console.WriteLine("start factorial with {0}", n);
            if (n == 0)
            {
                Console.WriteLine("factorial({0})={1}", n, 1);
                return 1;
            }

            int res = n * factorial(n - 1);
            Console.WriteLine("factorial({0})={1}", n, res);
            return res;
        }
    }
}