So i have spent the better part of a day now trying to work this out myself, however i feel I'm almost at the point where it's becoming counter productive, as I've tried everything i can think of, including using apt to install from the official repos and also downloaded source and built the library that way... I have actually installed GTK in the past, however this was some time ago and i remember having issues that time, but from memory, building from source fixed whatever problem i had back then.

Then i went to use the library again recently and it was not working, however i think i may have reinstalled Linux since then.
So i try install using apt, it just installs a bunch of other packages, and the #include in my C program does not find the library at all.
Then i download and build from source, my IDE recognizes the library, but none of the functions are recognized? I am using CLION, but i also had no luck trying to compile a program from the terminal.

What could i possibly be doing wrong?

This is compiler output.. But regardless of this, still none of the functions are recognized?

Code:
[ 50%] Building C object CMakeFiles/gtkz3.dir/main.c.o
In file included from /root/CLionProjects/gtkz3/main.c:1:0:
/usr/include/gtk-3.0/gtk/gtk.h:30:21: fatal error: gdk/gdk.h: No such file or directory
 #include <gdk/gdk.h>
                     ^
compilation terminated.
CMakeFiles/gtkz3.dir/build.make:62: recipe for target 'CMakeFiles/gtkz3.dir/main.c.o' failed
make[3]: *** [CMakeFiles/gtkz3.dir/main.c.o] Error 1
CMakeFiles/Makefile2:67: recipe for target 'CMakeFiles/gtkz3.dir/all' failed
make[2]: *** [CMakeFiles/gtkz3.dir/all] Error 2
CMakeFiles/Makefile2:79: recipe for target 'CMakeFiles/gtkz3.dir/rule' failed
make[1]: *** [CMakeFiles/gtkz3.dir/rule] Error 2
Makefile:118: recipe for target 'gtkz3' failed
make: *** [gtkz3] Error 2
I installed Curl, OpenSSL, and other libraries recently with no problem, i'm not sure why GTK always gives me so much trouble.