/*** 用recursive(遞迴)方式 求GCD(Greatest Common Divisor) ***/
//by Wen-Nung Tsai
#include <iostream.h>
#include <stdio.h>
#define repeat  do{
#define until(e)  }while(!(e))
#define mod %
long gcd(long m, long n);    /*求最大公因數*/
int main()
{
    long x,y;     /* 不叫 m,n 也沒關係啦 */
  cout << "Find GCD of two numbers. Program stops when one of the input is 0\n";
  repeat
     cout <<" First number=? ";
     cin >> x;   /* 輸入資料到變數 x */
     cout <<" Second number=? ";
     cin >> y;
     cout<< x <<" 和 "<<y<<" 的最大公因數= " << gcd(x,y) << endl;
  until(x*y ==0);   /* 做到 有一個是0後就不玩了 :-) */
  return 0;
}
long gcd(long m, long n)
  {       /**輾轉相除法**/
       if(n<0)  return gcd(m,-n);
       if(m<n)  return gcd(n,m);
       if(n==0) return m;
       return gcd(n, m mod n);
  }