#include <iostream>
using namespace std;

const double pi = 3.14159; // I know there is a built-in pi

class box {
    public:
        double length, width, height;
        box() {length = 1; width = 2; height = 3;}
        box(double l, double w, double h) {
            length = l;
            width = w;
            height = h;
        }
        double volume() {
            return length * width * height;
        }
};

class cylinder {
    public:
        double length, radius;
        cylinder() {length = 30.0; radius = 4.5;}
        cylinder(double l, double r) {
            length = l;
            radius = r;
        }
        double volume() {
            return pi * length * (radius * radius);
        }
};

int main() {
    char choice;
    bool validChoice;
    double x, y, z;

    cout << "Do you want to find the volume of: a) box or b) cylinder? ";
    choice:
    cin >> choice;

    if (choice == 'a')
        validChoice = true;
    else if (choice == 'b')
        validChoice = true;
    else
        validChoice = false;

    if (validChoice == true) {
        if (choice == 'a') {
            cout << "Enter a length, width, and height: ";
            cin >> x >> y >> z;
            box b1(x, y, z); // It seems kind of awkward to declare this here,
             // and not at the top of main()
            cout << "The volume of a box of those proportions is "
                << b1.volume()
                << "."
                << endl;
        }
        else if (choice == 'b') {
            cout << "Enter a length and a radius: ";
            cin >> x >> y;
            cylinder c1(x, y);
            cout << "The volume of a cylinder of those proportions is "
                << c1.volume()
                << "."
                << endl;
        }
    }
    else {
        while (validChoice == false) {
            cout << "\nThat is not a valid selection.\n"
                << "Please choose either a or b for box or cylinder: ";
            goto choice;
        }
    }

    return 0;
}