Abstract Classes and Pure Virtual Functions

#include <iostream>
#include <string>

// Define an abstract class Shape. Note that the abstractness is achieved by having at least one pure virtual function denoted by = 0 in the declaration.
class Shape {
public:
    virtual ~Shape() = default; // Adding a virtual destructor
    virtual double area() const = 0; // Pure virtual function for calculating the area
    virtual double perimeter() const = 0; // Pure virtual function for calculating the perimeter
};

// Define a Circle class that inherits from Shape
class Circle : public Shape {
public:
    // Constructor to initialize the radius
    Circle(double radius) : radius(radius) {}

    // Implement the area and perimeter functions
    double area() const override { // Note, that the override keyword is optional
        return 3.14 * radius * radius;
    }

    double perimeter() const override {
        return 2 * 3.14 * radius;
    }

private:
    double radius;
};

// Define a Rectangle class that inherits from Shape
class Rectangle : public Shape {
public:
    // Constructor to initialize the width and height
    Rectangle(double width, double height) : width(width), height(height) {}

    // Implement the area and perimeter functions
    double area() const override {
        return width * height;
    }

    double perimeter() const override {
        return 2 * (width + height);
    }

private:
    double width;
    double height;
};

int main() {
    Circle circle(5);
    Rectangle rectangle(4, 6);

    std::cout << "Circle Area: " << circle.area() << ", Perimeter: " << circle.perimeter() << std::endl;
    std::cout << "Rectangle Area: " << rectangle.area() << ", Perimeter: " << rectangle.perimeter() << std::endl;

    // Using a Shape pointer to a Circle object
    Shape* shape = new Circle(3);
    std::cout << "Shape Area: " << shape->area() << ", Perimeter: " << shape->perimeter() << std::endl;
    delete shape; // Always remember to delete dynamically allocated memory

    return 0;
}