程序代码：

int fun(int n)
{
  int a, b, r;
  static int gcd = 0;
  
  if (0 == gcd)    return gcd = n;

  a = gcd, b = n;
  while (r = a % b)
  {
    a = b, b = r;
  }
  
  return gcd = b;
}