Lec#7
July 24 1995

A concrete class is one that has code and of course a private section, lets 
consider the the array implementation of a list, note that I don't mean an 
array implementation of a linked list, I mean just a list.  This subclass of
int_list inherits all behavior that we have committed to for int_list.  i.e.
if int_list said that the find function returns -1, if the value searched 
for is not found, thats exactly what find in int_array_list class does also.

The pointer implementation of list presents some problems, since the interface 
with the application requires position of a node in some cases, the
code is written so that the list is searched for the node in the correct
position, but from the applications perspective it all works the same.

This is where we examin the int_list.h, int_array_list.h, int_pointer_list.h,
int_array_list.cc, int_pointer_list.cc, and the ltest.cc that tests it.