What p points to shouldn't be modified (but p can be changed to point to something else). q mustn't be changed to point to something else (but what it points t

What p points to shouldn't be modified (but p can be changed to point to something else). q mustn't be changed to point to something else (but what it points to can be changed -- except that in this particular example, q will point to a string constant, which shouldn't be modified). Both of the above.