We finish the course with a final example which pulls together  many  of
the  concepts we have seen in recent chapters.  The example is an imple-
mentation of a Line Editor which can be used to edit a specific  file  a
line  at a time.  At first sight this might seem a challenging prospect.
The chapter aims to show that, given suitable general  purpose  classes,
the  task  is in fact relatively easy. This should serve as a demonstra-
tion of the power of Abstract Data Typing as an approach to  programming
and should highlight the issues of encapsulation and re-use of code.

However, to order to build our Line editor we do need to briefly digress
for  a  moment to consider a final new topic - the issue of command line
arguments to C++ programs.