Another note about this: with the following code, you can only have one
linked list, in the whole program.  This is worth pointing out (briefly)
as part of their understanding of how C doesn't have classes.  One way of
looking at the difference between modules and classes is that with classes,
you can automatically make any number of the data objects.  (Although you
can defeat this by using "class variables" ('static' class members in C++
or java).)