月の日数を取得する

// 今月の日数を取得
NSDate *today = [NSDate date];
NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
NSRange range = [calendar rangeOfUnit:NSDayCalendarUnit
                               inUnit:NSMonthCalendarUnit
                              forDate:today];
NSInteger daysOfMonth = range.length;
NSLog(@"today:%@ daysOfMonth:%d", today, daysOfMonth);

実行結果

today:2013-08-14 05:17:08 +0000  daysOfMonth:31