I am working on C++ since last 4-5 years . Recently I have bought iphone and macbook and want do do some programming for iphone.
So I have started reading one book about Objective-C. I have also learn that we can program with Ruby and Python on MAC.
So my question is which one to study? Which language you guys see the FUTURE???
Can we program with these languages on other platforms? Or are these only limited on MAC?
I am just a beginner in objective-C.Need some expert thoughts which way to go.
AC
Which language you guys see the FUTURE???
Future of what?  iPhone development?  Objective-C.  
Web Services?  Python/Ruby in parallel for a while.  At least until people start trying to do maintenance on large Ruby applications and get frustrated with it's opacity.
Real-time game engine development?  Embedded applications?  Future of what?
"Can we program with these languages on other platforms? Or are these only limited on MAC?"
Ruby and Python: Yes.  These are designed to run on any platform that supports C.
Objective-C: Yes.  It's open source, it's in the GCC, it should work almost anywhere.  
Learning a new language is not a zero-sum game.  You can learn more than one language; learning Objective-C now does not prevent you from learning Python or Ruby in the future.
Study Objective-C , Ruby OR Python?