The Waite Group's C++ Primer Plus, Third Edition

Inheritance—An Is-a Relationship

Now that BankAccount has joined the ranks of the working class, you can derive a new class from it. Before doing so, however, let's examine the underlying model for C++ inheritance. Actually, C++ has three varieties of inheritance: public, protected, and private. Public inheritance is the most common form, and it models an is-a relationship. This is shorthand for saying that an object of a derived class should also be an object of the base class. Anything you do with a base-class object, you should be able to do with a derived-class object. Suppose, for example, you have a Fruit class. It could store, say, the weight and caloric content of a fruit. Because a banana is a particular kind of fruit, you could derive ...