Unfortunately you are not correct. Pointer arithmetic is only valid if the resulting calculated address is within the bounds of the same array as the original p

Unfortunately you are not correct. Pointer arithmetic is only valid if the resulting calculated address is within the bounds of the same array as the original pointer, or calculates an address that is just past the end of the array. Otherwise it is our old friend undefined behavior. See section 6.5.6 of the C11 spec.