gui/game librarys FOR C++
I'd also recommend SFML: http://www.sfml-dev.org/
Don't forget the docs: http://www.sfml-dev.org/resources.php
I think to remeber me that allegro some few ele ts provide like messageboxes but im not quite sure.
Do you really want use some gui libraries try an look at qt or simliar ones
For 3D, check out Urho3D:
https://github.com/urho3d/Urho3D
For the brief time I had looking over it, it looks very powerful and actually is easy to use (just build and run the examples to see what I mean).
Another great 3D library is Ogre3D:
If you find those overwhelming, you might want to consider starting with something far easier, but just as powerful:
For GUI, I recommend libRocket. It is general purpose, independent on other game engines, and can easily be adapted for OpenGL (which is what I did). On the negative side, it takes some effort to interface. On the positive side, it is very efficient and powerful. You will be able to control the GUI with a design similar to html and css.
you can try cocos2d-x, SFML, or if you not only need to build game but an application, try Qt
