When you define a C++ class, which of the following should be part of the implementation?

a. all declarations of private member variables
b. all declarations for public member functions
c. all explanatory comments for public member declarations.
d. all declarations for private member functions (auxiliary or helping functions)
e. all member function definitions, public and private (implementations of functions).

a) d) and e) are implementation.
Explanation: b) c) are interface. This is information needed to know what the class and its member do, but nothing that tells how the do “it”. The following are implementation: a) private member variables are part of the implementation, not the interface. d) Private member functions are part of the implementation not of the interface e) definitions of functions are part of the implementation not interface.