classes for a Q&A C++ application

[ariaHov]

Hello!
I want to create a Q&A console application in C++ which must allow management of different types of users(administrator, moderator topic, ordinary user)

I don't know how to start and I need a hint.
Which is the best way, to make a class for login or a class for users?

[boost lexical cast]

Class for users. That's about it. Inside the class the member functions should take care of the logins.