[Problem] Composition aka Writing programs in multiple files

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

Code:

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undefined reference to `...`

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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.

The problem is not with the headers, but that you are not linking to the object files generated from compiling the various source files that correspond to those headers. With Code::Blocks, this means that you probably did not put those source files in the project.

You have to options, either track dependencies on your own (write Makefile etc.) or rely on your IDE.

Review extern and static keywords. Also don't forget about include guards or #pragma once.