#include <iostream>
#include "prompt.h"
using namespace std;

// illustrates loop and integer overflow

long Factorial(int num);

int main()
{    
    int highValue = PromptRange("enter max value for factorial",1,30);
    int current = 0;  // compute factorial of this value
    
    while (current <= highValue)
    {   cout << current << "! = " << Factorial(current) << endl;
        current += 1;
    }
    return 0;
}

long Factorial(int num)
// precondition: num >= 0
// postcondition returns num!
{
    long product = 1;
    int count = 0;

    while (count < num)          // invariant: product == count!
    {   count += 1;
        product *= count;
    }
    return product;
}