I have this question and might look stupid indeed, but bear with me.
I have files in this hierrachy

ProjectFolder/Panel/panel.h
ProjectFolder/Panel/panel.cpp
AND
projectFolder/Search/search.h
projectFolder/Search/search.cpp

I want to include search.h in panel.h
I have tried many thing including

#include "./search/search.h"
#include "../search/search.h"

but I have failed. Any suggestion on how to do it right?

Solved it.
It was spelling error than anything else error. Just added project DIr to compiler search path and that is ;)