So I finished my first C++ programming assignment and received my grade. But according to the grading, I lost marks for including cpp files instead of compiling and li
The basic idea that headers are only included and cpp files are only compiled. This will become more useful once you have many cpp files, and recompiling the whole application when you modify only one of them will be too slow. Or when the functions in the files will start depending on each other. So, you should separate class declarations into your header files, leave implementation in cpp files and write a Makefile (or something else, depending on what tools are you using) to compile the cpp files and link the resulting object files into a program.