常用代码

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

[b]精确的时间差[/b]
NSTimeInterval begin = CFAbsoluteTimeGetCurrent();
...
NSTimeInterval gap = (CFAbsoluteTimeGetCurrent() - begin);

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

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