how to solve undefined reference error message

class Drawable
{
public :
    virtual void draw() = 0;
	virtual ~Drawable() {};
};
 
class MyDrawable : public Drawable
{
public :
    virtual void draw();
    MyDrawable();
    virtual ~MyDrawable();
private :
    int * data;
};
 
MyDrawable::~MyDrawable()
{
    delete data;
}
 
void MyDrawable::draw()
{
 
}
 
MyDrawable::MyDrawable()
{
    data = new int;
}
 
void del(Drawable* drawable)
{
    delete drawable;
}
 
int main()
{
    del(new MyDrawable());
}

class Drawable
{
public :
    virtual void draw() = 0;
	virtual ~Drawable() = 0;
};

Drawable::~Drawable()
{
}