So lately I've been writing multiple header and cpp files and I would always the same error when I finally #include headers in my main.cpp. This error
undefined reference to `...`
On Youtube videos I see people doing this and their work magically compiles correctly. I found out that when I #include the headers' cpp files instead, my programs would compile. I use Code::Blocks with GNU GCC compiler. Looking for someone with this problem and has solved it to give me some tips for this matter.