08_GreatestCommonDivisor

using System;

/*
 * 8. Write a program that calculates the greatest common divisor (GCD) of given two numbers.
 * Use the Euclidean algorithm.
 */
class GreatestCommonDivisor
{
    static void Main()
    {
        uint a;
        uint b;
        uint tmp;
        uint gcd;

        Console.Write("A = ");
        string strA = Console.ReadLine();

        Console.Write("B = ");
        string strB = Console.ReadLine();

        if (!uint.TryParse(strA, out a))
        {
            Console.WriteLine("Invalid number: {0}", strA);
        }
        else if (!uint.TryParse(strB, out b))
        {
            Console.WriteLine("Invalid number: {0}", strB);
        }
        else
        {
            if (a == 0 && b > 0)
            {
                gcd = b;
            }
            else if (b == 0 && a > 0)
            {
                gcd = a;
            }
            else if (a > 0 && b > 0)
            {
                while (b > 0)
                {
                    tmp = b;
                    b = a % b;
                    a = tmp;
                }

                gcd = a;

                Console.WriteLine("The GCD is {0}.", gcd);
            }
        }
    }
}