code organization style

[Gabor Szabo <szabgab gmail com>]

As I have just started to learn Gtk and never wrote anything more than one
simple window in Tk either I would like to get your opinion on how to
organize code ?

So far I have an application with several windows all in one file of
over 1000 rows.
It is getting too big for one file so I am think of splitting it up
and puting each
popup window in a separate class.

Also the main window has two panes, both of the are TreeViews and are getting
complex so I think I should put each one of the in a separate class.

How do you people do it ?
Where can I see examples ?

Gabor