怎么wa了
帮忙该一下吧
#include <stdlib.h>
#include <stdio.h>
#include <math.h>

double lnchoose(int n, int m)
{
    if (m > n)
    {
        return 0;
    }
    if (m < n/2.0)
    {
        m = n-m;
    }
    double s1 = 0;
    for (int i=m+1; i<=n; i++)
    {
        s1 += log((double)i);
    }
    double s2 = 0;
    int ub = n-m;
    for (int i=2; i<=ub; i++)
    {
        s2 += log((double)i);
    }
    return s1-s2;
}

double choose(int n, int m)
{
    if (m > n)
    {
        return 0;
    }
    return exp(lnchoose(n, m));
}

int main()
{
    int n,m;
    while(scanf("%d %d",&n,&m) && n && m)
    {
        double res=choose(n,m);
        printf("%d things taken %d at a time is %.lf exactly.\n",n,m,res);
    }
}