./gtkcc foo foo.c
or just ./gtkcc foo.c (will compile to foo)
see for details: https://developer.gnome.org/gtk3/3.2/gtk-getting-started.html
gtkcc is a helper for the following command:
gcc `pkg-config --cflags gtk+-3.0` -o foo foo.c `pkg-config --libs gtk+-3.0`
run chmod +x makeln && chmod +x gtkcc && ./makeln gtkcc
to make gtkcc executable without the ./ prefix and from any directory