I am trying to write a program in C and I need the gtk/gtk.h file, which I both currently don't appear to have nor am I sure how to get it.
When I compile all I get is cannot find the file, how can I resolve this issue?
search the newest libgtk-dev file in the debian package repository and download it.
gtk.h should be in the package.
If you really want to code using gtk I would suggest you start by looking here for tutorials. I would really suggest you use vala or python for any gui work though, c is not really the best choice for this task.
As to the files you need. They are contained within the