deleting object of polymorphic class type 'shape' which has non-virtual destructor might cause undefined behavior [-Wdelete-non-virtual-dtor]

shape *p1 = new circle(3.2);	shape *p2 = new rect(4.6,5.2);	p1->jsmj();	p2->jsmj();	delete p1	p1 = NULL;	delete p2;	p2 = NULL;	return 0;