(C++) question about GUI's?

I'm currently in my 2nd semester of C++ (Object Oriented C++) and going to take a 3rd C++ cl next semester (Data Structures and Algorithms taught in C++). The one thing I noticed so far, and it's still early in the 2nd semester, is that it seems pure C++ isn't good for developing a GUI. I was told that I should just start learning Visual C++ in my spare time since it's real easy to make GUI's ... but the thing is I'm more interested in Linux and from what I gather Visual C++ is more for making windows apps? Is there a multi-platform compiler thats good for GUI's as well as linux/windows/mac apps without favoring one system over the next?