/*
  Ken Moore 2003 - polymorphism
*/
#include <iostream>
#include <string>
using namespace std;

class shape{
protected:
	double area;
public:
	shape():area(0){}
	shape(double a):area(a){}
	// pure virtual version
	// precludes instantiating shape
	// virtual void computeArea() = 0;

	// not pure virtual, shape can be instantiated 
	virtual void computeArea(){};

	// without virtual in prototype:
	// no polymorphism
	virtual void show(string s)const{
		cout << s << endl;
		cout << "in shape " << endl;
		cout << "area = " << area << endl;
	}
};

class rect:public shape{
	int x1, y1, x2, y2;
public:
	rect():shape(-1){}
	rect(int a, int b, int c, int d):x1(a),y1(b),x2(c),y2(d){
		area = (x2 - x1)*(y2 - y1);
	}
	void computeArea(){area = (x2 - x1)*(y2 - y1);};
	void show(string s)const{
		cout << s << endl;
		cout << "in rect " << endl;
		cout << "area = " << area << endl;
		cout << " x1 y1 " << x1 << " " << y1 << endl;
		cout << " x2 y2 " << x2 << " " << y2 << endl;
	}
};
class circle:public shape{
	int x, y;
	double radius;
public:
	circle():shape(-1){}
	circle(int a, int b, double r):x(a),y(b),radius(r){
		area = 3.14159*radius*radius;
	}
	void computeArea(){area = 3.14159*radius*radius;};
	void show(string s)const{
		cout << s << endl;
		cout << "in circle " << endl;
		cout << "area = " << area << endl;
		cout << " x y " << x << " " << y << endl;
		cout << " radius " << radius << endl;
	}
};

void main(){
	// try "shape s();" instead of "shape s;" 
	// and see what happens - 
	// compiler thinks it is a function prototype!
	shape s;
	s.show("show default shape variable ");
	rect r(0,0,2,4);
	r.show("show 0,0,2,4 rectangle");
	circle c(10,10,1.0);
	c.show("show circle");

	// show "slicing" problem
	s = r;

	s.show("variables polymorphic? y if rect n if shape!");

	// not allowed
	//int *ip = new int(3);
	//double *dp = new double(2.71);
	//dp = ip;

	// perfectly ok?
	shape *sp, *sp2 = new shape();
	rect  *rp = new rect(0,0,2,4);
	circle *cp = new circle(10,10,1.0);
	sp = rp;

	// show how different elements can be
	// late bound via polymorphism
	sp->show("show rect via shape pointer");
	shape *sps[3];
	sps[0] = sp2;
	sps[1] = rp;
	sps[2] = cp;
	for(int i = 0; i < 3; i++)
		sps[i]->show("testing polymorph");
}