abstract_base_class.cpp

#include <iostream>
#include <string>
using namespace std;

// Abstract base class
class Shape {
public:
    // Pure virtual function (must be overridden in derived classes)
    virtual double area() = 0; // Declared but not defined, = 0 indicates it's pure

    virtual string getType() = 0;

    virtual ~Shape() {} // Virtual destructor
};

// Derived class 1
class Circle : public Shape {
private:
    double radius;
public:
    Circle(double r) : radius(r) {}

    double area() override {
        return 3.14159 * radius * radius;
    }

    string getType() override {
      return "Circle";
    }
};

// Derived class 2
class Rectangle : public Shape {
private:
    double width;
    double height;
public:
    Rectangle(double w, double h) : width(w), height(h) {}

    double area() override {
        return width * height;
    }

    string getType() override {
      return "Rectangle";
    }
};

int main() {
    // Create pointers to Shape (abstract class)
    Shape* shape1 = new Circle(5.0);
    Shape* shape2 = new Rectangle(4.0, 6.0);

    // Polymorphism: Calling area() through the base class pointer, but the correct derived class method is executed
    cout << "Area of " << shape1->getType() << ": " << shape1->area() << endl; // Calls Circle::area()
    cout << "Area of " << shape2->getType() << ": " << shape2->area() << endl; // Calls Rectangle::area()

    delete shape1;
    delete shape2;

    return 0;
}