GTK+ is a GUI library for C and a bunch of other languages. Recently, I had the "pleasure" of installing this on Windows 7. Follow these steps and you'll be compiling GTK C programs in no time.
Download the GTK+ bundle for windows (32 or 64bit), I used 32 bit because my MinGW is 32bit.
Install in a simple directory like C:\opt\ or F:\opt\
Go to your windows environment variables on your computer and add GTK's bin directory to the PATH variable. eg. C:\opt\bin
Execute both of these commands on the command line:
pkg-config --cflags gtk+-2.0
pkg-config --libs gtk+-2.0
If the above commands fail to produce outputs than your install is bad, you need to reinstall or check your PATH variable.
Next, run package config and store the result into a file using the output direction '>'
pkg-config --cflags --libs gtk+-2.0 > flags.txt
Copy the contents of flags.txt into your makefile or use on the command line
The compile line should look like this:
gcc -o main main.c -mms-bitfields -IF:/opt/include/gtk-2.0 -IF:/opt/lib/gtk-2.0/include -IF:/opt/include/atk-1.0 -IF:/opt/include/cairo -IF:/opt/include/gdk-pixbuf-2.0 -IF:/opt/include/pango-1.0 -IF:/opt/include/glib-2.0 -IF:/opt/lib/glib-2.0/include -IF:/opt/include -IF:/opt/include/freetype2 -IF:/opt/include/libpng14 -LF:/opt/lib -lgtk-win32-2.0 -lgdk-win32-2.0 -latk-1.0 -lgio-2.0 -lpangowin32-1.0 -lgdi32 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lpango-1.0 -lcairo -lgobject-2.0 -lgmodule-2.0 -lgthread-2.0 -lglib-2.0 -lintl
GTK should now be setup for windows, happy coding.
P.S. When compiling object files using gcc -c you only need to link in the cflags files.
Using the method above, but only with: pkg-config --cflags gtk+-2.0