iOS 判断iphone ipad 系统版本

#define ScreenWidth  ([[UIScreen mainScreen] bounds].size.width)
#define ScreenHeight ([[UIScreen mainScreen] bounds].size.height)

#define iOS8 ([[[UIDevice currentDevice] systemVersion] floatValue] >= 8.0)
#define iOS7 ([[[UIDevice currentDevice] systemVersion] floatValue] >= 7.0)
#define iOS6 ([[[UIDevice currentDevice] systemVersion] floatValue] >= 6.0)

#define isPad   (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad   ? YES : NO)
#define isPhone (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPhone ? YES : NO)
#define isRetina ([[UIScreen mainScreen] scale] > 1 ? YES : NO)

原文：http://my.oschina.net/qianglong/blog/330163