poj 1306 Combinations

#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>using namespace std;long long com(long long n, long long r){    if (n - r < r)        r = n - r;    long long i, j, s = 1;    for (i = 0, j = 1; i < r; ++i)    {        s *= (n - i);        for (; j <= r && s % j == 0; ++j) s /= j;    }    return s;}int main(){    long long m, n;    while (scanf("%lld%lld", &m, &n), m | n)        printf("%lld things taken %lld at a time is %lld exactly.n", m, n, com(m, n));    return 0;}