An application compiled for iOS 6 launches in a special compatibility mode on iOS 7.
When compiling with Xcode 5, you must support at least iOS 7. By setting “Deployment Goal”, you can also support older versions, but if you use the features available only in iOS 7, you must first check if the application crashes on iOS 6 .
Also note that the various user interface components on iOS 7 have different sizes than on iOS 6. You need to service this either with Interface Builder (possibly with autostart) or in your code. How to do this is described in detail in the iOS 7 Transition Guide .
The simplest solution is to support only iOS 7. The best option completely depends on your circumstances, customer base, etc.
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