Person : Show some basic use, with syntax, of member functions,
                      and restriction on private member access.
===============================================================

This example shows how classes can be defined and used.  Our Person
class is defined in person.h, implemented in person.cpp, and used by
the (client) code in main.cpp.

Notice that the client #includes the Person header, where the member
functions of the Person class are declared.  So the client can _use_ the
functionality exposed by the public member functions of that class.  But the
client main _has no visibility of how these functions are implemented_.  That 
is, the implementation machinery of the class is private.  The data is declared
as private, and the functions are only used, not seen at source-level by their
client(s).

This provides all sorts of benefits.  For example, the member function 
implementations can be changed without necessarily impacting on client code.
Provided the member function names, parameter, and return types remain 
unaltered, client code does not need to be changed, or even recompiled.  
It only needs to be re-linked to the updated object code of the classes that it 
uses.  This reduction in dependency can greatly reduce build times in program
development and maintenance.  It also allow the programming workload to be 
divided along natural boundaries, and carried out in distinct, coherent, parts
- possibly at different times, and/or in parallel by different people.

This example shows how constructors can be declared, defined, and used; and how
member functions can similarly be declared, defined, and called by objects of
their class. 

See the source files, and also the xxx...line_by_line files for person.h, 
person.cpp, and main.cpp for detailed explanations of what is done in this
example, and how.


Build notes
==============

To build, at the command prompt enter the line:

g++ main.cpp person.cpp -o person


Then to run it, use:

./person, or a similar invocation for whatever name you have chosen to 
          call your program

