LinuxProgramming.com: Utilizing Callbacks in Gtk+

“Having an attractive layout to your application is only one
part of your design process; you need to make your program do
something! The something depends on your application. In the case
of our calculator from the last article, it looks, well, like a
calculator (except that the display is centered, which will be
fixed today). But it doesn’t act like a calculator. Right now
clicking on the buttons causes no difference in appearance except
for whatever visual cues GTK+ is giving that the buttons are being
pressed, and no calculations occur. Not a very useful calculator,
no matter how aesthetically pleasing it might be. Thus, the
topic of today’s article: adding functionality to your application.
In the case of GTK+, functionality comes in the form of functions
that are invoked in response to signals emitted by a
widget.”

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