第二周任务二：自定义求阶乘

#include<iostream>   using namespace std;  long fac(int n)//求 N的阶乘  {     int j = 1;      while ( n > 0 )     {                  j = j * n;          n--;          }     return j; }  int main() {     int m,n,C_mn;      cout << "请输入m,n的值" << endl;      cin >> m >> n;      C_mn = fac(m)/( fac(n)*( fac(m-n) ) );      cout << "所求组合数为" << C_mn << endl;              return 0; }