求组合数

#include <iostream>
#include<stdio.h>
using namespace std;

int main()
{
    int r,n,ans,t;
    scanf("%d%d",&n,&r);
    if(n-r<r)
    r=n-r;
    ans = n;
    n=n-1;
    t=2;
    while(t<=r)
    {
        ans=ans*n/t;
        n--;
        t++;
    }
    printf("%d\n",ans);
    return 0;
}