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Fortunately, C++ encourages you to cut down on duplication, thereby easing program writing, debugging, and maintenance, by allowing you to arrange class definitions in hierarchies that reflect natural category hierarchies.
Using C++, you can say, for example, that box cars, tank cars, engines,
and cabooses are railroad cars. Then, you can declare a year_built
member variable and an age member function in the
railroad_car class alone, because the year_built member
variable will appear in each individual box car, tank car, engine, and
caboose object, and the age member function will be available to all
those railroad_car objects as though age had been declared four
times.