Hello,
I'm mostly programming in PHP and C#, but I have some experience (pretty basic) in C++. The most "complicated" thing I created was a window with some buttons and lists on it (using Win32 API), and playing with classes.
Now, I want to get deeper into C++ - creating multi-platfrom (Windows, Linux, or even Mac if that is possible).
When I want to open a file I can use Win32 API, but now, do I have to write the same code 2/3 times (for each OS)? And what about the GUI? What can I use and what not? Which IDE to use?
Can anyone give me an online website or anything that can help me begin?

Thanks,
Ori Lahav.