>> SPEAKER 1: It turns out this program, short though it is,
actually has a bug.
In rare circumstances, GetString, per its own documentation, can return
something other than a string.
Specifically, a sentinel, a special value called null--
N-U-L-L.
>> Null signifies that generally, something went wrong whereby in this
case, the user might have typed in such a big string that it wouldn't fit
in memory, and so GetString might return null in that case.
>> Or it might be that the user somehow didn't type any string at all, in
which case no string can come back.
So it's best that we detect whether or not null has
been returned as follows--
Only if S does not equal null should I proceed to execute this loop.
>> In other words, if GetString happens to return null, I'm not going to
accidentally try iterating over characters that simply are not there.