常用代码

Degrees,Radians相互转换
CGFloat DegreesToRadians(CGFloat degrees) {return degrees * M_PI / 180;};
CGFloat RadiansToDegrees(CGFloat radians) {return radians * 180 / M_PI;};

精确的时间差
NSTimeInterval begin = CFAbsoluteTimeGetCurrent();
...
NSTimeInterval gap = (CFAbsoluteTimeGetCurrent() - begin);

得到year,month,day,week,weekday
NSDateComponents *components = [[NSCalendar currentCalendar] components:NSYearCalendarUnit | NSMonthCalendarUnit | NSDayCalendarUnit | NSWeekdayCalendarUnit fromDate:targetDate];

[components year];
[components month];
[components day];
[components week];
[components weekday];