In how many ways can you choose k elements out of n elements, not taking order into account?
Write a program to compute this number.

The input will contain one or more test cases.

Each test case consists of one line containing two integers n (n>=1) and k (0<=k<=n).

Input is terminated by two zeroes for n and k.

For each test case, print one line containing the required number. This number will always fit into an integer, i.e. it will be less than 2
³¹.

Warning: Don't underestimate the problem. The result will fit into an integer - but if all intermediate results arising during the computation will also fit into an integer depends on your algorithm. The test cases will go to the limit.

4 2

10 5

49 6

0 0

6

252

13983816


求C（n,k),模板题

#include<iostream>

#include<string>

#include<cstdio>

#include<algorithm>

#include<cmath>

#include<cstring>

using namespace std;

#define ll long long

#define M 105

ll n,k;

int main()

{

    ll i,j;

    while(cin>>n>>k)

    {

        if(n==0&&k==0)

            break;

        if(k==n)

        {

            cout<<1<<endl;

            continue;

        }

        if(n-k<k)

            k=n-k;

        ll ans=1;

        for(i=1;i<=k;i++)

        {

            ans=ans*(n-i+1)/i;

        }

        cout<<ans<<endl;

    }

}