How to declare the area and volume function

Question

#include <iostream>
using namespace std;

class Shape {
        protected:
        int _w, _h;
        public:
        Shape(int w, int h) : _w(w), _h(h) { }
//declaration of area and volume function
};

class Rectangle : public Shape {
        public:
        Rectangle(int w, int h) : Shape(w, h) { }
};

class Cube : public Shape {
        public:
        int _b;
        public:
        Cube(int w, int h, int b) : Shape(w, h), _b(b) { }
        int area() { return 2 * (_w * _h + _w * _b + _b * _h); }
        int volume() { return _w * _h * _b; }
};

int main() {
    Shape *pt;
    int w, h, b, v;
    cin >> w >> h >> b;
    pt = new Rectangle(w, h);
    cout << pt->area() << " ";
    if ((v = pt->volume()) == -1)
        cout << "Undefined ";
    else
        cout << v << " ";
    pt = new Cube(w, h, b);
    cout << pt->area() << " ";
    if ((v = pt->volume()) == -1)
        cout << "Undefined ";
    else
        cout << v << " ";
}

for the input 4 5 8 the output will be 20 Undefined 184 160 and in another test case the input is 10 20 10 and the output is 200 Undefined 1000 2000 how to declare and define area() and volume() to satisfy the given test cases.

Answer 1

Welcome to SO.

I believe what you are looking for is how to declare the two functions for your two inherited classes, Rectangle and Cube.

The general topic that you can look into is called 'polymorphism', where the parent class can take many forms through its derived classes.

Here is an example of what you might be inclined to do, but won't work as intended:

class Shape {
   protected:
      int width, height;

   public:
      Shape( int a = 0, int b = 0){
         width = a;
         height = b;
      }
      int area() {
         cout << "Parent class area :" <<endl;
         return 0;
      }
      int volume() {
         cout << "Parent class volume:" <<endl;
         return 0;
      }
};

What will happen if you run the code above is the parent's area and volume functions may run in ill-defined cases instead. This is because the program will try to do static linking on the functions, basically gluing them in place and preventing us from changing them.

We want to be able to change the area and volume functions to match our derived class, so what you will need to do instead, is to define your area and volume functions as 'virtual' in your parent class, like so:

class Shape {
   protected:
      int width, height;

   public:
      Shape( int a = 0, int b = 0){
         width = a;
         height = b;
      }
      virtual int area() {
         cout << "Parent class area :" <<endl;
         return 0;
      }
      virtual int volume() {
         cout << "Parent class volume:" <<endl;
         return 0;
      }
};

The virtual functions will force the derived classes, such as rectangle or cube, to provide their own functions for those base functions, by telling the program we want to let the derived classes provide the functions instead.

Please have a look at the Stack Overflow post here for more details if you have questions in the future. They have many answers that elaborate on the subject, if there is anything I have missed here.

Hope these help you understand how to handle polymorphism better.