我总是将这些保存在我的Constants.h文件中：

I always keep those in my Constants.h file:

#define IS_IPHONE5 (([[UIScreen mainScreen] bounds].size.height-568)?NO:YES) 
#define IS_OS_5_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 5.0)
#define IS_OS_6_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 6.0)
#define IS_OS_7_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0)
#define IS_OS_8_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0)
#define IS_OS_9_OR_LATER    ([[[UIDevice currentDevice] systemVersion] floatValue] >= 9.0)

虽然我总是喜欢上面的宏，但是为了完成接受的答案，这是苹果批准的方式：

Although I'll always prefer the above macros, for the completion of the accepted answer, here is the apple approved way:

if (NSFoundationVersionNumber > NSFoundationVersionNumber_iOS_6_1) {

    // do stuff for iOS 7 and newer

}
else {

    // do stuff for older versions than iOS 7
}