C++ class redefinition error - Help me understand headers and linking

Question

I started writing a simple interpreter in C++ with a class structure that I will describe below, but I quit and rewrote the thing in Java because headers were giving me a ha

Answer 1

Why can I #include a million times, even one after the other, but I can only include my header once?

It is probably because your header doesn't have an include guard.

// printer.h file
#ifndef PRINTER_H_
#define PRINTER_H_

 // printer.h code goes here

#endif

Note that it is best practice to chose longer names for the include guard defines, to minimise the chance that two different headers might have the same one.