#include <iostream>

using namespace std;

int factorial(int);
void choose(int,int,int&);

int main()
{
    int n, k, result;

    n = 10;
    k = 1;
    result = 0;
    choose(n, k, result);
    cout << "n: " << n << endl;
    cout << "k: " << k << endl;
    cout << "result: " << result << endl;
    return 0;
}

//
// Description: calculates x!
// Pre: x is greater than or equal to zero
// Post: returns x factorial
//
int factorial(int x)
{
    int result = 1;

    if (x < 0)
    {
        cout << "ERROR: (x < 0) in factorial(x)" << endl;
        assert(x >= 0);
    }
    if (x == 0)
    {
        return 1;
    }

    // We know (x > 0)
    while (x > 1)
    {
        result = result * x;
        x--;
    }

    return result;
}

//
// Description: calculates N choose K
// Pre: n and k are both greater than or equal to 0
// Post: myResult contains the value of N choose K
//
// NOTE: THERE'S A BUG HERE!
//
void choose(int n, int k, int& myResult)
{
    assert((n >= 0) && (k >= 0));
    k = 2;
    myResult = factorial(n) / (factorial(k) * factorial(n - k) );
    return;
}