Virtual Functions and Polymorphism

Runtime Dispatch

Add virtual to a base class method so derived overrides are called through a base pointer:

class Animal {
public:
    virtual string speak() { return "..."; }
    virtual ~Animal() {}   // always virtual destructor!
};

class Dog : public Animal {
public:
    string speak() override { return "Woof!"; }
};

Animal* a = new Dog();
cout << a->speak();   // "Woof!" — correct at runtime!
delete a;

Pure virtual — abstract classes

class Shape {
public:
    virtual double area() = 0;   // must override in subclass
    virtual ~Shape() {}
};
// Cannot instantiate Shape directly

Your Task

Create abstract Shape with pure virtual area() and perimeter().
Implement Rectangle (w, h) and Circle (r).
Write totalArea(vector<Shape*> shapes).