Assignment makes the pointer point to a different object

int i = 42;
int *pi = 0; // pi is initialized but addresses no object
int *pi2 = &i; // pi2 initialized to hold the address of i
int *pi3; // if pi3 is defined inside a block, pi3 is uninitialized
pi3 = pi2; // pi3 and pi2 address the same object, e.g., i
pi2 = 0; // pi2 now addresses no object