(1)    求最大公约数

     欧几里得算法:

            gcd( int m, int n)

             {

                  int t,r;

                  if(m<n) {t=m; m=n; n=t;}

                  while(n!=0)

                  {

                     r=m%n;

                     m=n;

                     n=r;

                   }

                   return m;

          }