Preface O bjective-C is this object-oriented extension to C.You learning Objective-C Objects." an could call it "C with If you're reading book, you're probably interested in so that you can write applications for Mac OS X or for iOS. But there's another reason to learn Objective-C: It's a fun language and one that is relatively easy to learn. Like anything else in the real world, Objective-C has some rough spots, but on the whole it is a much simpler language than other object-oriented languages, particularly C++. The additions that Objective-C makes to C can be listed on a page or two. In the Apple world, Objective-C does not work alone. It is used in conjunction with two class libraries called frameworks. The Foundation framework contains classes for basic entities, such as strings and arrays, and classes that wrap interactions with the operating system. The AppKit contains classes for windows, views, menus, buttons, and the assorted other widgets needed to build graphical user interfaces. Together, the two frameworks are called Cocoa. On iOS, a different framework called the UIKit replaces the AppKit. Together, Foundation and UIKit are called Cocoa Touch. Objective-C was initially created by Brad J. Cox in the early 1980s. In 1988, NeXT Computer, the company started by Steve Jobs after he left Apple, licensed Objective-C and made it the basis of the development environment for creating applications to run under NeXT's NeXTSTEP operating system. The NeXT engineers developed a set of Objective-C libraries for use in building applications. After NeXT withdrew from the hardware business in 1993, it worked with Sun Microsystems to create OpenStep, an open specification for an object-oriented system, based on the NeXTSTEP APIs. Sun eventually lost interest in OpenStep. NeXT continued selling its version of OpenStep until NeXT was purchased by Apple in early 1997. The NeXTSTEP operating system became the basis of Mac OS X. The NeXT Objective-C libraries became the basis of Cocoa. This book concentrates on the Objective-C language. It will not teach you how to write Cocoa programs or make you an expert Xcode user. It covers and makes use of a small part of the Foundation framework, and mentions the AppKit and UIKit only in passing. The book's premise is that you will have a much easier time learning Cocoa if you first acquire a good understanding of the language on which Cocoa is based. Who Should Read This Book This book is intended for programmers who want to learn Objective-C in order to write programs for Mac OS X or iOS. (iOS is used for the iPhone, the iPod touch, and the iPad.) Although it is technically possible to write complete OS X programs using