Programming in Mac

If you're learning for fun it honestly doesn't really matter what language you learn as it's the core concepts that are actually important when it comes to programming. There are workarounds to write/compile C# or VB on OSX (look up something called mono), but it might be easier for you to simply learn a different language.

Java is very similar to C# and will run/compile on Mac as well as windows.

As the others say, just use a vm if you want to use Visual Basic for stuff like C, but if you wanted to learn java use eclipse, really depends on what language you want to learn.