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;