Determine number of cars built from parts

// Determine the number of cars you can
// build with the parts you have.
// axles, wheels, bodies
//
// TEST INPUT
// Test One: 10 axles, 60 wheels, 17 bodies makes
// 5 cars with left over: 0 axles, 40 wheels, 12 bodies
// Test Two: 38 axles, 68 wheels, 25 bodies makes
// 17 cars with left over: 4 axles, 0 wheels, 8 bodies
// Test Three: 341 axles, 273 wheels, 67 bodies makes
// 67 cars with left over: 207 axles, 5 wheels, 0 bodies

#include <iostream>
#include <string>

using namespace std;

const int axles_per_car = 2; // A car has two axles.
const int wheels_per_car = 4; // A car has four wheels.
const int bodies_per_car = 1; // A car has one body.

// This function does two things:
// 1) returns the number of complete cars that can be
// built with the axles, wheels and bodies given.
// 2) determines the number of leftover parts.
int make_cars(int axles, int wheels, int bodies,
    int& leftover_axles, int& leftover_wheels, int& leftover_bodies)
{
    // Determine how many cars you can build with just the axles.
    int num_possible_cars_axles = axles / axles_per_car;
    // Determine how many cars you can build with just the wheels.
    int num_possible_cars_wheels = wheels / wheels_per_car;
    // Determine how many cars you can build with just the bodies.
    int num_possible_cars_bodies = bodies / bodies_per_car;

    // Assume we have enough parts to use all the axles.
    // We could build half as many cars as we have axles
    // 2 axles per car
    int max_num_cars = num_possible_cars_axles;
    // If we don't have enough wheels to build this many cars
    // Update the number of cars we can build with the wheels.
    if (num_possible_cars_wheels < max_num_cars)
    {
        max_num_cars = num_possible_cars_wheels;
    }
    // If we don't have enough bodies to build this many cars
    // Update the number of cars we can build with the bodies.
    if (num_possible_cars_bodies < max_num_cars)
    {
        max_num_cars = num_possible_cars_bodies;
    }

    // Calculate how many leftover axles, wheels and bodies we have.
    leftover_axles = axles - (axles_per_car * max_num_cars);
    leftover_wheels = wheels - (wheels_per_car * max_num_cars);
    leftover_bodies = bodies - (bodies_per_car * max_num_cars);

    return max_num_cars; // Return the number of cars we can build.
}

int main()
{

    string num_axles_string; // User input axles.
    string num_wheels_string; // User input wheels.
    string num_bodies_string; // User input bodies.
    int num_axles = 0; // axles converted to integer.
    int num_wheels = 0; // wheels converted to integer.
    int num_bodies = 0; // bodies converted to integer.
    int leftover_axles = 0; // Number axles leftover.
    int leftover_wheels = 0; // Number wheels leftover.
    int leftover_bodies = 0; // Number bodies leftover.
    int cars_built = 0; // Number of complete cars built.

    cout << "This program will tell you how many "
        "cars can you build from the parts you have.\n";

    cout << "For each car, you need :\n"
        "2 axles\n"
        "4 wheels\n"
        "1 body\n";

    cout << "\nHow many axles do you have? ";
    getline(cin, num_axles_string); // Get number of axles.

    cout << "\nHow many wheels do you have? ";
    getline(cin, num_wheels_string); // Get number of wheels.

    cout << "\nHow many bodies do you have? ";
    getline(cin, num_bodies_string); // Get number of bodies.

    // Convert axles, wheels and bodies strings to integers.
    num_axles = stoi(num_axles_string);
    num_wheels = stoi(num_wheels_string);
    num_bodies = stoi(num_bodies_string);

    // Determine how many cars can be built with the parts we have.
    cars_built = make_cars(num_axles, num_wheels, num_bodies,
        leftover_axles, leftover_wheels, leftover_bodies);

    // Display the result.
    cout << "\nYou can build " << cars_built << " cars.\n";
    cout << "\nYou have left over:\n";
    cout << leftover_axles << " axles\n";
    cout << leftover_wheels << " wheels\n";
    cout << leftover_bodies << " bodies\n";

    return 0; // End the program.
}