private static void userDatesAndTimes()
{
System.Console.WriteLine("=> Dates and Times:");
// datetime constructor
DateTime dt = new DateTime(2021, 10, 17);
// day?
System.Console.WriteLine($"the day of {dt.Date} is {dt.DayOfWeek}");
// month?
dt = dt.AddMonth(2);
System.Console.WriteLine($"Daylight savings: {dt.isDayLightSavingTime()}");
// time constructor
TimeSpan ts = new TimeSpan(4, 30, 0);
System.Console.WriteLine(ts);
// time difference: t1 - t2
System.Console.WriteLine(ts.Subtract(new TimeSpan(0, 15, 0)));
}