Here’s where we’ve been heading and why you’ve been reading this book – writing iOS and Cocoa apps. In the next two chapters, you’ll get a taste of application development. Your applications will have a GUI (graphical user interface), and they will be event-driven.

In a command-line program, you execute the program, and then it does its own thing until it’s all finished. An event-driven application is different. It launches and then starts a run loop which waits for events. When an event happens, the application leaps into action, executing methods, sending messages, etc.

First, you’ll write an iOS application and then a similar Cocoa application. Cocoa is the collection of frameworks written by Apple that you use to write applications on the Mac. You’re already familiar with one of these frameworks – Foundation.

To write iOS apps, you use another set of frameworks called Cocoa Touch. Cocoa and Cocoa Touch have some frameworks in common, like Foundation. Others are specific to one platform or the other.