/////////////////////////////////////////////////////
//
// assertions.cpp
//
// Jeff Ondich, 4/7/04
//
// A simple example of the use of an assertion to
// verify a precondition.
//
/////////////////////////////////////////////////////

#include <iostream>
#include <assert.h>
using namespace std;

int factorial( int n );

int main()
{
    int n = 0;
    cout << "Number, please: ";
    cin >> n;

    cout << n << "! = " << factorial( n ) << endl;

    return 0;
}

// Returns the factorial of the specified integer.
// Precondition: n >= 0 and n < 13.

int factorial( int n )
{
    assert( n >= 0  &&  n < 13 );
    
    if( n == 0 )
        return 1;

    return n * factorial( n - 1 );
}