#include <cstdio>
#include <cstdlib>

class Shape {
public:
  Shape(){
    printf("Shape() constructor\n");
    xPos = 5;
    yPos = 5;
  }

  virtual void draw() const = 0;

  double perimeter() const {
    return(0);
  }

  double getX() { return xPos; }
  double getY() { return yPos; }

protected:
  double xPos;
  double yPos;
};

class Triangle : public Shape {
public:

  Triangle() {
    printf("Triangle() constructor\n");
    xPos = 2;
    yPos = 2;
  }

  virtual void draw() const {
    printf("This is a triangle!\n");
  }

};

int main(int argc, char* argv[])
{

/*
  Shape* s = new Shape;
  s->draw();
  printf("The x-coordinate of s is %lg\n", s->getX());

  Triangle* t = new Triangle;
  t->draw(); // equivalent to (*t).draw();
  printf("The x-coordinate of t is %lg\n", t->getX());
*/

  // Say I'm writing a graphics library
/*
  Shape* allTheShapes[1000];
  allTheShapes[0] = new Triangle;
  allTheShapes[1] = new Square;
  for(i = 0; i < 1000; i++){
    allTheShapes[i]->draw()
  }
*/

  // C++ does not allow this; Triangle may require
  // more memory than Shape and not fit in the same slot
  //Shape x = Triangle();

  // So instead we use pointers
  Shape* r = new Triangle;
  r->draw();


  //delete s;
  //delete t;
  delete r;

  return(0);
}