problem with if + %.

Console.WriteLine("This is a program that calculates the gcd of some typed number");
            int StartingNum = Convert.ToInt16(Console.ReadLine());
            int NumForCalculate = StartingNum;
            string gcd = ("");
            int gathering = 1;
            operation:
            int x = 2;
            operation2:
            if ((NumForCalculate / x) == :see below:)
            {
                if (gcd == "")
                    gcd = ("" + x);
                else
                    gcd = (gcd + "," + x);
                NumForCalculate = (NumForCalculate / x);
                gathering = gathering * x;
                if (NumForCalculate <= 1)
                    goto end;
                else
                    goto operation;
            }
            else
            {
                x++;
                goto operation2;
            }
            end:
            Console.WriteLine("gcd of integers {0} is {1}, and gathering this set of numbers is {2}", StartingNum, gcd, gathering);
            Console.ReadKey();