判斷ios7系統和屏幕尺寸大小

#define IS_IPHONE_5 (fabs((double)[[UIScreen mainScreen] bounds].size.height - (double)568)

#define IOS7 [[UIDevice currentDevice].systemVersion floatValue] >= 7.0
#define screenWidth     [UIScreen mainScreen].bounds.size.width
#define screenHeight    [UIScreen mainScreen].bounds.size.height