C++ file extensions:

• .cpp
• .CC
• .cxx

C++ header file extensions

• .hpp
• .h
• hxx

The recommended extensions are .cpp and .hpp

• The selection of a file extensions usually comes down to preference or versions of software you're using

The output of the compiled code comes out as a .o file

Preproccesed C++ Source Files have a .ii file extension

A class in C++ is a user-defined type or data structure declared with any of the keywords class, struct, or union

• By default access to members of a C++ class declared with the keyword class is private. The private members are not accessible outside the class; they can be accessed only through member functions of the class
• The public members form an interface to the class and are accessible outside the class.