Highlights
what is this #include? GROSS! Well, it tells the C Preprocessor to pull the contents of another file and insert it into the code right there. ^ref-40543
Wait—what’s a C Preprocessor? Good question. There are two stages26 to compilation: the preprocessor and the compiler. Anything that starts with pound sign, or “octothorpe”, (#) is something the preprocessor operates on before the compiler even gets started.
your source runs through the preprocessor, then the output of that runs through the compiler, then that produces an executable for you to run
your source runs through the preprocessor, then the output of that runs through the compiler, then that produces an executable for you to run