title: Is NULL always zero in C?
body: <p>I was interviewing a guy for a mid-level software engineering position yesterday, and he mentioned that in C, NULL is not always zero and that he had seen implementations of C where NULL is not zero. I find this highly suspect, but I want to be sure. Anyone know if he is right? </p>
  
  <p>(Responses will not affect my judgement on this candidate, I've already submitted my decision to my manager.)</p>