I am working on an application in which I need to migrate the whole code of it from carbon to cocoa.I have experience in programming of C,C++,python and Java during my college t
First, learn Carbon so you can read the program and understand how it's currently implemented.
Install the Legacy documentation set in Xcode to gain access to the Carbon guides. You'll want to read the Carbon Overview, then Getting Started with Carbon, then everything that Getting Started links to. You'll also need to learn Core Foundation, which some of the more modern parts of Carbon use; read Core Foundation Design Concepts and the Memory Management Programming Guide for Core Foundation.
Then, learn Cocoa.
I didn't learn by the Hillegass book, but a lot of people swear by it. My current favorite Cocoa book is “Cocoa and Objective-C: Up and Running” by Scott Stevenson. The way I learned Cocoa was using Apple's own docs. Start with The Objective-C Programming Language, the Cocoa Fundamentals Guide, and the Memory Management Programming Guide for Cocoa. Much of the last document will seem really familiar, but skip nothing. Read every one of those guides from beginning to end and all the way through.
Once you've learned Cocoa's general concepts, you can move on to more application-specific material. Start with the Application Architecture Overview and most of what that document links to. The Cocoa Guides list has the full list of guides.
Down the road, you'll also need to make the application compatible with 64-bit mode. If you still have any Carbon code by that point, you'll need to read the 64-bit Guide for Carbon Developers; either way, you'll also need the general 64-bit Transition Guide and the 64-bit Transition Guide for Cocoa.