int *q = new int(42), *r = new int(100);
r = q;r and q points to the same memory, while the old memory pointed by r is leaked, since no pointer points to it and it is not freed.
auto q2 = make_shared<int>(42), r2 = make_shared<int>(100);
r2 = q2;First, the reference count of r2 is decreased, and the memory pointed by r2 is freed, since no shared_ptr points to it. Second, r2 and q2 point to the same memory, and the reference count of both smart pointers are increased.