Final answer:
The question deals with applying inheritance in a C++ program to create a hierarchy of cipher classes, with all derived ciphers inheriting from a substitution cipher class or one of its derivatives.
Step-by-step explanation:
The question relates to the implementation of a substitution cipher using inheritance in C++ programming. Since a substitution cipher class has been defined (but not implemented) in cipher.h and cipher.cc, other cipher classes must inherit either directly from the substitution cipher class or from one of the other cipher classes that derive from it.
For example, a Caesar cipher would inherit from the substitution cipher class, while ROT13, a specific type of Caesar cipher, could inherit from the Caesar class itself.
This creates an inheritance hierarchy in object-oriented programming, where cipher classes share certain properties and methods from their parent classes, but also introduce their own unique functionality. The concept is essential as it promotes code reuse, modularity, and polymorphism in the application's design.
The subject of this question is Computers and Technology. The student is asking about the inheritance structure for the cipher classes. They need to either inherit from the Substitution cipher class or inherit from one of the four other cipher classes, such as Caesar or ROT13, which inherit from Substitution. This question pertains to programming and software development.