// 當前時間創建NSDate

    NSDate *myDate = [NSDate date];

    NSLog(@"myDate = %@",myDate);

    //從現在開始的24小時

    NSTimeInterval secondsPerDay = 24*60*60;

    NSDate *tomorrow = [NSDate dateWithTimeIntervalSinceNow:secondsPerDay];

    NSLog(@"myDate = %@",tomorrow);

    //根據已有日期創建日期

     NSTimeInterval secondsPerDay1 = 24*60*60;

    NSDate *now = [NSDate date];

    NSDate *yesterDay = [now addTimeInterval:-secondsPerDay1];

    NSLog(@"yesterDay = %@",yesterDay);

    

    //比較日期

    BOOL sameDate = [now isEqualToDate:yesterDay];

    NSLog(@"sameDate = %lu",sameDate);

    //獲取較早的日期

    NSDate *earlierDate = [yesterDay earlierDate:now];

    NSLog(@"earlierDate  = %@",earlierDate);

    //較晚的日期

    NSDate *laterDate = [yesterDay laterDate:now];

    NSLog(@"laterDate  = %@",laterDate);



    //兩個日期之間相隔多少秒

    NSTimeInterval secondsBetweenDates= [yesterDay timeIntervalSinceDate:now];

    NSLog(@"secondsBetweenDates=  %lf",secondsBetweenDates);

    //通過NSCALENDAR類來創建日期

    NSDateComponents *comp = [[NSDateComponentsalloc]init];

    [comp setMonth:06];

    [comp setDay:01];

    [comp setYear:2001];

    NSCalendar *myCal = [[NSCalendaralloc]initWithCalendarIdentifier:NSGregorianCalendar];

    NSDate *myDate1 = [myCal dateFromComponents:comp];

    NSLog(@"myDate1 = %@",myDate1);

    

    //從已有日期獲取日期

    unsigned units  = NSMonthCalendarUnit|NSDayCalendarUnit|NSYearCalendarUnit;

    NSDateComponents *comp1 = [myCal components:units fromDate:now];

    NSInteger month = [comp1 month];

    NSInteger year = [comp1 year];

    NSInteger day = [comp1 day];

    //NSDateFormatter實現日期的輸出

    NSDateFormatter *formatter = [[NSDateFormatteralloc]init];

    [formatter setDateStyle:NSDateFormatterFullStyle];//直接輸出的話是機器碼

    //或者是手動設置樣式[formatter setDateFormat:@"yyyy-mm-dd"];

    NSString *string = [formatter stringFromDate:now];

    NSLog(@"string = %@",string);

    NSLog(@"formater = %@",formatter);