#include <iostream>
using namespace std;
 
// Shape is abstract class: some methods are already available, some are not
class Shape
{
public:
// This is already implemented and ready for polymorphism
virtual void area() { cout<<"Shape area"<<endl;}
// You MUST implement this
virtual void implement_me() = 0;
};
 
class Circle : public Shape
{
public:
virtual void area() { cout<<"Circle area"<<endl;}
void implement_me() { cout<<"I implemented it just because I had to"<<endl;}
};
 
class HalfCircle : public Circle
{
public:
virtual void area() { cout<<"HalfCircle area"<<endl;}
};
 
 
// ShapeInterface is a pure class or interface: everything must be implemented!
class ShapeInterface
{
public:
virtual void area() = 0;
};
 
class CircleFromInterface : public ShapeInterface
{
public:
// You MUST implement this!
virtual void area() { cout<<"CircleFromInterface area from interface"<<endl;};
};
 
 
 
int main() {
 
	Shape* ptr_to_base = new HalfCircle();
	ptr_to_base->area(); // HalfCircle area, polymorphism
	ptr_to_base->Shape::area(); // Shape area
	ptr_to_base->implement_me(); // from Circle
 
 
	ShapeInterface *ptr_to_base_int = new CircleFromInterface();
	ptr_to_base_int->area(); // Just the derived has it
 
	return 0;
 
 
}

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