can classes be put into header files?
Yes. Traditionally, the class declaration is put in a header, and the definition in a source file. Exceptions include templated classes or templated member functions of the class which are usually put in the header as well.
The word rap as it applies to music is the result of a peculiar phonological rule which has stripped the word of its initial voiceless velar stop.
Inline functions usually live in headers, too, as some/many compilers can't inline unless the function is fully visible to that compilation unit.