iPhone SDK uses the Objective-C language, which is an extension to the C language. Like any other mobile, iPhone too has a different programming platform; Windows Mobile (VB.NET/C#) and Android (Java) use object-oriented languages and are identical in syntax. However, Objective-C takes a totally different approach. Being different it creates a learning barrier especially for beginners dealing with Mac OS for the first time.

Objective-C as implemented by Apple is built entirely around Objects. It is used throughout the iPhone OS’s frameworks. Windows, views, buttons, sliders and controllers exchange information with each other in the form of events and actions in order to make the program run.

A header file (.h) and a source code (.m) file together represent each object in Objective-C. iPhone OS frameworks provide many standard classes that come with the framework, but sometimes you may have to write your own subclasses. When you do this, you’ll need a new header and source code class together to represent the new subclass in your project.

The iPhone OS is divided in to four layers (Cocoa touch, Media, Core Services, Core OS), as represented in the diagram. Each layer contains variety of frameworks that you can use in your application/program. Initially, you would be dealing with the top layer.

• Cocoa touch - the base framework, that you will deal most of the time. It contains the UI-Kit framework which includes window support, event support and user-interface management.
• Media – the framework that provide the protocols to deal with audio and video build in iPhone.
• Core Services – the frameworks used in all applications, data types.
• Core Operating System – the kernel level software. Dealing with threading, networking, I/O, memory etc…