I have been using Mac for a while and I am a senior CS major. I want to start making apps for Mac however I dont know where to start. Currently I know java, c++ , c , python as my main languages. Do I need to learn another language like objective-c ? Can anyone point me to a place to start ?
Well, the first two things you will need to do is learn how to use Xcode and then you will need to learn Objective-C.
To learn how to use Xcode, I would start with the Xcode Workspace Guide
To learn Objective-C, Apple has a great, free book - The Objective-C Programming Language. The one aspect of Objective-C which makes it easier to learn for many is that it is a true superset of C (C++, for example, is not). If you already know C, Objective-C just adds a little bit to support objects.
Then, I would pick up a copy of Cocoa(R) Programming for Mac(R) OS X (3rd Edition) by Aaron Pablo Hillegass. This book is the standard for starting out to learn Cocoa and build real Mac applications.