http://kor.i2p/books/The%20C%20Programming%20Language%20by%20K&R/chapter5.html
First, pointers may be
compared under certain circumstances. If p and q point to
members of the same array, then relations like == , != , < , > = , etc., work properly. For example, p < q is true if p points to an earlier element of the array than q does.