c++ 추상클래스 공부하다 막혀서 질문드립니다.

#ifndef SAHPE_H
#define SAHPE_H
 
#include <iostream>
using namespace std;
 
class Shape{
	int index;
	Shape* next;
public:
	Shape();
	void paint();
	Shape* add(Shape* p, int index);
	Shape* getNext() {return next;}
	int getIndex();
	virtual void draw()=0;
	virtual ~Shape();
};
#endif

#include "Shape.h"
 
Shape::Shape(){
	index = 0;
	next = NULL;	
}
 
void Shape::paint(){
	draw();
}
 
Shape* Shape::add(Shape *p, int index){
	this->index = index;
	this->next = p;	
	return p;
}
 
int Shape::getIndex(){
	return this->index;
}
 
Shape::~Shape(){
	if(next)
		delete next;
}