What is the easiest way to make Linux C++ GUI apps? I'm using GNOME and ubuntu 8.10.
I personally prefer QT as I prefer working with the signal/slots mechanism and just find it easy to develop applications quickly with it. Some of your other options would be wxWidgets and GTK+.
Try QT, it will work on Ubuntu, and has a lot of development tools and documentation behind it.
I can personally vouch for the ease of use of qt in general, as well as linux specific development. CHeck it out :)
The easiest way is to use an GUI GUI builder.
Glade for GTK.
QT Designer for QT.
wxDesigner and wxFormBuilder for wxWidgets.
Update: I should mention that these output C++ among many others?
Just to be clear about the toolkits mentioned so far (GTK+,QT and wxWidgets)
GTK+ is the toolkit used by GNOME
QT is the toolkit used by KDE
wxWidget aims to be an abstraction above those (and others) to be less desktop environment specific.
Another toolkit worh takeing a peek at is EFL the toolkit used by E17, although the glacier development speed of this desktop environment may put you off, I hear nice things about it's design. Note that some components from the Enlightenment project such as imlib2 has been used for years by other projects.
I suggest Juce. It's elegant, cross-platform, fast, well-written, almost totally bug-free and is identical to the last pixel on every platform it runs on. The number of known bugs is nearly always zero, since when a bug report is filed, the author drops everything and fixes it! The Register wrote an article about it a while ago which gives a rather good overview of the library.