There were no less than SEVEN files in the example I wrote to show a "simple" demonstration of polymorphism in C++ yesterday ...
1. The methods for a base class of file objects - Film.cpp
2. The extra methods on top of the base class for a derived class of Blockbuster objects - Blockbuster.cpp
3. The extra methods on top of the base class for a derived class Cinema.cpp
4. The header file Film.h, for inclusion in each of the above
5. The header file Cinema.h for inclusion in that extended class and the test application
6. The header file Blockbuster.h for inclusion in that extended class and the test application
7. The test application - flix.cpp
Why so many files?
a) Because C++ is a language that is designed for the larger application, and it's not really intended for tiny programs such as this - the seven files are indeed a lot to start off with, but the code can be extended from this trivial job up to something much MUCH bigger.
b) Because each of the sections might be maintained by a separate programmer and so it's a good structure through which that maintainance can be done independently
c) Because the use of header files which are included in two or more of the sections of program allows the programmers to maintain a single set of method descriptions rather than duplicated code, with all the synchronisation and extra headaches that might bring.
And these are all excellent reasons, aren't they?
The complete example is in our source code library. But I have NOT put all seven files up separately, to produce a heptagonal array of extra window when you click on the link ... just click here for a single extra window containing all the source
to see the whole example in one go. (written 2008-06-12)
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Destructor methods in C++ - a primer - (2011-11-05) 
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Objects and Inheritance in C++ - an easy start - (2010-07-01) 
Complete teaching example - C++, inheritance, polymorphism - (2010-01-15) 
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