using System;

​

namespace FunWithDates

{

    // DateTime studies after DST headache

    public class DateArithmetic

    {

        public static DateTime AddSubtractDays(DateTime theDate, int numDays)

        {

            DateTime returnValue = theDate;

            returnValue.AddDays(numDays);

            return returnValue;

        }

​

        public static DateTime AddSubtractDaysCorrect(DateTime theDate, int numDays)

        {

            DateTime returnValue = theDate.AddDays(numDays);

            return returnValue;

        }

​

        public static DateTime AddSubtractDaysShort(DateTime theDate, int numDays)

        {

            return theDate.AddDays(numDays);

        }

​

        public static DateTime AddSubtractDays2(DateTime theDate, int numDays)

        {

            DateTime returnValue = theDate.AddDays(numDays);

            return returnValue;

        //return returnValue;

        }

​

        public static void Main()

        {

            DateTime date1, date2;

            DateTimeOffset dateOffset1, dateOffset2;

            TimeSpan difference;

            // Find difference between Date.Now and Date.UtcNow

            date1 = DateTime.Now;

            Console.WriteLine("DateTime.Now is " + DateTime.Now);

            Console.WriteLine("Current Timezone is " + TimeZone.CurrentTimeZone.StandardName);

            date2 = DateTime.UtcNow;

            difference = date1 - date2;

            Console.WriteLine("{0} - {1} = {2}", date1, date2, difference);

            // Find difference between Now and UtcNow using DateTimeOffset

            dateOffset1 = DateTimeOffset.Now;

            dateOffset2 = DateTimeOffset.UtcNow;

            difference = dateOffset1 - dateOffset2;

            Console.WriteLine("{0} - {1} = {2}", dateOffset1, dateOffset2, difference);

            // If run in the Pacific Standard time zone on 4/2/2007, the example

            // displays the following output to the console:

            //  4/2/2007 7:23:57 PM - 4/3/2007 2:23:57 AM = -07:00:00

            //  4/2/2007 7:23:57 PM -07:00 - 4/3/2007 2:23:57 AM +00:00 = 00:00:00

            Console.WriteLine("Next, Steve's subtract and hour from Ed's code");

            Console.WriteLine("Add 3 days " + AddSubtractDays(date1, 3).ToString());

            Console.WriteLine("Add 3 days " + AddSubtractDaysCorrect(date1, 3).ToString());

            Console.WriteLine("Add 3 days (no local var) " + AddSubtractDaysShort(date1, 3).ToString());

            Console.WriteLine("After which, the date variable itself is unchanged as " + date1.ToString());

        }

    }

}