Lecture 30

intcell_onefile.cpp show an implementation of the simple IntCell class, which acts
as a wrapper for an int value. The class definition appears in the same file
as the code that uses it.

intcell_better.h and intcell_better.cpp give a slightly better, but still flawed,
implementation. The definition of the class has been separated out, and placed
in a header file named intcell_better.h.

intcell.h and intcell.cpp give the appropriate definition of a class. The function
prototypes are given in the header file intcell.h, and the implementation of the class
has been separated out and placed in intcell.cpp. The file intcell_tester.cpp uses
the class to test its functionality.