I am doing research on PC vs Mac for unix
That was a rather open question.
As long as the language is standards-based, you should have no problem using the language on any platform where it's certified.
That said, anything related to utilising specific operating-system related features such as GUI are much different, except in Java. Since Java is the same output regardless of platform (but version-specific), you can run it on any platform with the correct version (usually the same or newer) Java Virtual Machine.
As mentioned, Java programming is the same on almost any platform. Traditionally, Macs lagged way behind Windows as far as Java releases are concerned, but the lag a lot less now (a few months, sometimes less). Macs also are much more Java-friendly.
Non-Java GUI programming is, as mentioned, much different. Honestly, enough tools exist on both platforms to make GUI programming similar in experience, though much different in actual code.
C, C++ both program the same on either platform (again, GUI code will be platform-specific).
A giant plus to Mac programming is that you have access to all the UNIX-type stuff in a way which is a part of the OS, as opposed to on a PC, where it all needs to be added on. I love the Terminal app on OS X - nothing like it on PCs.
Finally, if you're backed by someone with money, the tools on PCs are a bit better than what OS X has to offer, but not substantially.