How do I get my 1280Mega to recognise files in subfolders?

Hi, bit of a random noob question.
Basically I’m refering to #include
I have the following file structure:


Pic.h

Pic2.h

Now if I put in my project.
#include “Pic.h” //This works fine
#include “Pic2.h” //This returns not found
#include “SubFolder/Pic2.h” //This works fine

Now if I add Pic2.h as a file, it will be seen by #include “Pic2.h” whilst the file is open but if I close it again it starts to fail.

How do I get the software to recognise the file in the subfolder perminantly without having the file open or adding the subfolder inside the #include?

or adding the subfolder inside the #include?

Why is that a problem?

It’s not that it’s a problem its just anoying.