C++ header files store the following:
Class-independent data structures
In other words, anything that is not code goes into a header file. This means that you’ll probably need to protect the files against multiple inclusion, as detailed in Chapter 14.
This example assigns the header files the standard .h extension, much as you would a normal C header file. Some implementations will use .hpp to associate the filename with C++ rather than C, but this is not necessary.
Try to keep OO code and application startup code as separate as possible, and limit each header file to prototyping a single class.
It is worth noting, because you’ll likely come across an example ...