用C++怎么编写？一个理科女不会做

![img](https://img-mid.csdnimg.cn/release/static/image/mid/ask/15836701146614.jpeg "#l

#include <iostream>
using namespace std;
long long fact(int n)
{
    long long sum =  1;
    for(int i=1;i<=n;i++)
        sum *= i;
    return sum;
}
int main()
{
    int n,m;
    cin>>n>>m;
    printf("%lld",fact(n)/(fact(m)*fact(n-m));
}