uva solve problem 369 _combinations

#include<cstdio>
#include<algorithm>
using namespace std;
double permutation(long int n,long int r)
{
    int i,k;
    double num;
    if(r==0)
    return 1;
    k=min(r,n-r);
    num=1;
    for(i=k;i>=1;i--)
    {
        num=num*(n-i+1);
        num=num/i;
    }
    return num;
}
int main()
{
    long int n,r;
    double g;
    while(scanf("%ld%ld",&n,&r)==2)
    {
        if(n==0&&r==0)
        break;
        g=permutation(n,r);
        printf("%ld things taken %ld at a time is %.0lf exactly.\n",n,r,g);

    }
    return 0;
}