Question

using c# visual studio 2008.

Can anyone help with an algorithm to do this please

if i have a range of days selected for this week (eg monday to friday) i can find the dates for these using the datetime functions available.

What i want to do is compared to stored data for the same DAY range 1 year ago.

So basicly i need to go back 1 year and find the dates for the nearest Mon to fri DAY range from 1 year previous. I guess i also need to take into acount leap years.

Can anyone help with a suitable algorithm on how to achieve this.
Of course the DAY for todays date last year is not going to be the same day.

thanks in advance

Answer 1

Here’s some code which might do what you want – but the test cases show that there are corner cases to consider:

using System;

public class Test
{
    static void Main()
    {
        Console.WriteLine(SameDayLastYear(DateTime.Today));
        Console.WriteLine(SameDayLastYear(new DateTime(2010, 12, 31)));
    }

    static DateTime SameDayLastYear(DateTime original)
    {
        DateTime sameDate = original.AddYears(-1);
        int daysDiff = original.DayOfWeek - sameDate.DayOfWeek;
        return sameDate.AddDays(daysDiff);
    }
}

What would you want the result for the second call to be? This code returns January 1st 2010, because that’s the closest date to “a year ago on the same day”.

I strongly suggest that whatever you go with, you have unit tests checking leap years, start and end of year etc.