Volume returns 0 when called. Supposed to return 8

Question

Good morning! I have to do this for an exercise:

Since the Square and Cube geometric figures are drawn from points, write a program that defines the Point, Square, and Cube classes. Proceed using inheritance;

So I think I did well? Anyway, I hope... However, there is a part that does not seem to work, the volume

#include <iostream>
#include <conio.h>
#include <ctype.h>
#include <stdio.h>
 
using namespace std;
 
//########### Définition de la classe Point ###########
class Point {
    public:
        Point(int x, int y) {
            this->x = x;
            this->y = y;
        }
 
        int getX() {
            return x;
        }
 
        int getY() {
            return y;
        }
 
    private:
        int x, y;
};
 
//########### Définition de la classe Carré ###########
class Square : public Point {
    public:
        Square(int x, int y, int side) : Point(x, y) {
            this->side = side;
        }
 
        int getArea() {
            return side * side;
        }
 
    private:
        int side;
};
 
 
//########### Définition de la classe Cube ###########
class Cube : public Square {
    public:
        Cube(int x, int y, int side) : Square(x, y, side) {
 
        }
 
        int getVolume() {
            return side * side * side;
        }
 
    private:
        int side;
};
 
 
int main() {
 
    Cube cube(1, 1, 2);
 
    cout << cube.getX() << endl; // 1
    cout << cube.getY() << endl; // 1 
    cout << cube.getArea() << endl; // 4 
    cout << cube.getVolume() << endl; // 8 
 
    return 0; 
}

But I don't know why it returns 0 in the volume :'c It should be simple though! It's just an int of the side * side * side;

But when i run it it shows me 1 1 4 0

Why does this happend to the cube.getVolume()?

IMHO Not a great exercise for inheritance. Inheritance implies an “is-a” relationship. A square is not a point and a cube is not a square. — Mark Tolonen, Oct 27 '22 at 02:20
[What is a debugger and how can it help me diagnose problems?](https://stackoverflow.com/questions/25385173/what-is-a-debugger-and-how-can-it-help-me-diagnose-problems) — Jesper Juhl, Oct 27 '22 at 06:15

score 3 · Answer 1 · answered Oct 27 '22 at 00:59

Your Cube subclass overrides the variable side. So you now have two "side" values: Square::side and Cube::side. The latter is never initialized.

If you were to simply remove Cube::side, then you have an access problem because Square::side is declared private. If you want Cube to access that member, it should be protected instead.

class Point {
    public:
        Point(int x, int y)
            : x(x)
            , y(y)
        { }
 
        int getX() const { return x; }
        int getY() const { return y; }
 
    protected:
        int x, y;
};

class Square : public Point {
    public:
        Square(int x, int y, int side)
           : Point(x, y)
           , side(side)
        { }
 
        int getArea() const { return side * side; }
 
    protected:
        int side;
};
 
class Cube : public Square {
    public:
        Cube(int x, int y, int side)
            : Square(x, y, side)
        { }
 
        int getVolume() const { return side * side * side; }
};

score 0 · Answer 2 · answered Oct 27 '22 at 01:20

I would like to add that, since you have declared the variable side in Square class as private, Cube can not inherit from super class Square. So you can just assign the value of side in the constructor of Cube. Or make side of Square accessible to inherited class.

#include <iostream> 
#include <ctype.h>
#include <stdio.h>
 
using namespace std;
 
//########### Définition de la classe Point ###########
class Point {
    public:
        Point(int x, int y) {
            this->x = x;
            this->y = y;
        }
 
        int getX() {
            return x;
        }
 
        int getY() {
            return y;
        }
 
    private:
        int x, y;
};
 
//########### Définition de la classe Carré ###########
class Square : public Point {
    public:
        Square(int x, int y, int side) : Point(x, y) {
            this->side = side;
        }
 
        int getArea() {
            return side * side;
        }
 
    private:
        int side;
};
 
 
//########### Définition de la classe Cube ###########
class Cube : public Square {
    public:
        Cube(int x, int y, int side) : Square(x, y, side) {
            this->side = side;
        }
 
        int getVolume() {
            return side * side * side;
        }
 
    private:
        int side;
};
 
 
int main() {
 
    Cube cube(1, 1, 2);
 
    cout << cube.getX() << endl; // 1
    cout << cube.getY() << endl; // 1 
    cout << cube.getArea() << endl; // 4 
    cout << cube.getVolume() << endl; // 8 
 
    return 0; 
}

Volume returns 0 when called. Supposed to return 8

2 Answers2