You're not supposed to programmatically quit iOS apps.
Don’t Quit Programmatically
Never quit an iOS app programmatically because people tend to interpret this as a crash. However, if external circumstances prevent your app from functioning as intended, you need to tell your users about the situation and explain what they can do about it. Depending on how severe the app malfunction is, you have two choices.
Display an attractive screen that describes the problem and suggests a correction. A screen provides feedback that reassures users that there’s nothing wrong with your app. It puts users in control, letting them decide whether they want to take corrective action and continue using your app or press the Home button and open a different app
If only some of your app's features are unavailable, display either a screen or an alert when people use the feature. Display the alert only when people try to access the feature that isn’t functioning.
That being said, you can call
exit(0) but it's highly not recommended. http://stackoverflow.com/questions/1707685/how-to-quit-an-iphone-app-nicely