Caution: Sometimes 0 != NULL (Score 1)

Never rely on 0 being a reasonable value for pointers. Use NULL.

I've seen too many programs segfault on AMD64 just because some lazy programmer wrote "0" as a pointer value to save typing the three more characters required to type "NULL". "0" is a 32 bit integer which turns out to be NOT equal to "NULL", a 64 bit pointer.