// HW08_2c.java
// Tim Hilby
// Created on April 12, 2006
import java.util.Scanner;

public class HW08_2c
{
   // calculates the gcd
   public static int gcd(int num1, int num2)
   {
      // return num2 if num2 <= num1 and num2 divides num1
      if ((num2 <= num1) && (num1 % num2 == 0))
      {
         return num2;
      }
      // return gcd(num2, num1) if num1 < num2
      else if (num1 < num2)
      {
         return gcd(num2, num1);
      }
      // return gcd(num2, num1 % num2) otherwise
      else
      {
         return gcd(num2, num1 % num2);
      }
   }

   public static void main(String[] args)
   {
      Scanner scan = new Scanner(System.in);
      
      System.out.print("This program calculates the ");
      System.out.println("greatest common divisor");
      System.out.println("of two positive numbers.");
      
      int a = 0;
      int b = 0;
      System.out.println("Enter the two numbers: (0 to quit)");
      a = scan.nextInt();
      // don't bother reading the second number if the first is 0
      if (a != 0)
      {
         b = scan.nextInt();
      }
      while ((a != 0) && (b != 0))
      {
         if ((a < 0) || (b < 0))
         {
            System.out.println("Both numbers must be positive!");
         }
         else
         {
            System.out.println("Answer: " + gcd(a, b));
         }
         System.out.println("Enter the two numbers: (0 to quit)");
         a = scan.nextInt();
         // don't bother reading the second number if the first is 0
         if (a != 0)
         {
            b = scan.nextInt();
         }
      }
   }
}