Muhammad: I have merged your two threads into a single discussion (previously there was one copy in Game Programming and one in General Programming). In the future, please do not post multiple copies of the same topic in different forums.

Thanks!

I never coded a single bit of C# in my life, however I do have quite some experience with GUI coding (in C++) using wxWidgets, which I think totally rocks. But since I can't compare from own experience: what makes coding GUIs in C# a better choice over C++ with wxWidgets?

the simple fact that you can use a language that has the constructs needed for nice event handling built in the language itself (ie. delegates) as opposed to a language where these constructs have to be simulated using preprocessing hacks (QT) or some other convoluted system simply to use a member function as a callback.
Also the built in reflection and metadata in C# makes it much easier to build a visual gui editor.
But the real answer to your question is 3 clicks and 15 minutes of coding away.. that is.. download Visual C# and see yourself... it really just takes 10 minutes and a simple 1 button application (WinForm) to convince yourself there is no real comparison.

the simple fact that you can use a language that has the constructs needed for nice event handling built in the language itself (ie. delegates) as opposed to a language where these constructs have to be simulated using preprocessing hacks (QT) or some other convoluted system simply to use a member function as a callback.
Also the built in reflection and metadata in C# makes it much easier to build a visual gui editor.

The same goes for Objective-C/Cocoa, or Python/Kivy. Of course, all these options place certain limitations on portability.

Would a C# project also work (i.e. be compilable) for other platforms than Windows? And more specifically, does it give native controls (i.e. Windows look & feel on Windows, OS X look & feel on OS X, etc) on the supported platforms?

a simple WinForm application will run, without recompiling, under Mono on lots of different platforms.

Having said that, I dont see the issue of portability raised by the OP. The typical usage of a GUI application in the game development industry is for tools, and who really cares about portability of a tool? Hardly a show stopper for these kind of applications where the main discriminant is productivity and robustness, and rightly so.

I agree, for beginners C# forms is the way to learn. For C++ QT is very good, and it supported by all major platofrms; even mobiles. GTK+ is quite good, but more lower level and harder to understand at the beginning. With these GUI APIs you can create some really useful tools, which will aid you in the future when you develop games (making your own game editors, etc).

Get to grips with raw C++; bare in mind as ApochPiQ mentioned isn't GUI development friendly. So write some console apps, and when you are ready and you have covered not only C++ programming; you have also learned the structure of a program. Once you get to writing GUI applications, knowing about message queueing, events, input, GUI interaction will come with patience and most importantly persistance.

Agree with the previous posts MFC is absolutely terrible, do not bother. I've heard good things about WX as well. To be honest, there are plenty of alternatives; These GUI's are good bases to learn when you are ready. Just to add, a lot of in-game menus (HUDs) and GUI are usually done with Crazy Eddie's GUI, which not only uses C++, but also easier languages like C#, Python, and many more . Look at the video demos for now, once you get more acclimatised to more graphical programming, remember it and give the code examples a try.