what is a good gui library that I should use?

Please try doing your own research more often instead of opening a thread for each question you have. You will find enough information on that topic yourself.

However, the problem with most GUI engines that I know (Qt, wxWidgets) is, that using OpenGL with them is not as straight forward as it could be. Until you get everything running as desired, it will take some more or less complicated setup steps and I am not sure if you are up to the task if I see the problems you are facing in all your other threads. You should probably get more experience with OpenGL and C++ first before trying to add a GUI engine to your project that will make everything much more complicated. But I'll guess that won't stop you from doing it anyways.

Greetings

5 hours ago, DerTroll said:

However, the problem with most GUI engines that I know (Qt, wxWidgets) is, that using OpenGL with them is not as straight forward as it could be.

I think it is not a good idea to use Qt and wxWidgets for games. He will spend a lot of time these frameworks but at the end he will understand that he need to load fonts (BMFont or FreeType) and he need to make his own buttons. It is not to complicated to make buttons. You can just load textures and draw them on rectangles to make letters and buttons.

50 minutes ago, 8Observer8 said:

I think it is not a good idea to use Qt and wxWidgets for games.

Didn't say he should. Actually, I adviced against it. I used them just for editors and it was quite a pain to set everything up so that I can use my own render engine instead of the inbuilt Qt OpenGL interfaces.

Greetings