//GCDCalc.java

import java.util.Scanner;

public class GCDCalc
{
    /* Determine the greatest common divisor
       of two numbers, e.g. GCD(8, 12) = 4
    */
    public static int gcdCalculator(int inNum1, int inNum2)
    {
        int gcdVal; // Holds GCD results

        if (inNum1 == inNum2) // Base case: Numbers are equal
        {
            gcdVal = inNum1;  // Return value
        }
        else // Recursive case: subtract smaller from larger
        {
            if (inNum1 > inNum2) // Call function with new values
            {
                gcdVal = gcdCalculator(inNum1 - inNum2, inNum2);
            }
            else // n1 is smaller
            {
                gcdVal = gcdCalculator(inNum1, inNum2 - inNum1);
            }
        }

        return gcdVal;
    }

    public static void main (String[] args)
    {
        Scanner scnr = new Scanner(System.in);
        int gcdInput1; // First input to GCD calc
        int gcdInput2; // Second input to GCD calc
        int gcdOutput; // Result of GCD

        // Print program function
        System.out.println
        (
            "This program outputs the greatest \n"
            + "common divisor of two numbers."
        );

        // Prompt user for input
        System.out.print("Enter first number: ");
        gcdInput1 = scnr.nextInt();

        System.out.print("Enter second number: ");
        gcdInput2 = scnr.nextInt();

        // Check user values are > 1, call recursive GCD function
        if ((gcdInput1 < 1) || (gcdInput2 < 1))
        {
            System.out.println("Note: Neither value can be below 1.");
        }
        else
        {
            gcdOutput = gcdCalculator(gcdInput1, gcdInput2);
            System.out.println
            (
                "Greatest common divisor = "
                +  gcdOutput
            );
        }
    }
}