Date Diff By Ignoring Leap Days

Question

Please share some logic to find date difference between two dates which would ignore leap days, c# Subtract method includes the leap days. E.g. for startDat= 26-02-2016 and endDate= 03-03-2016 I want answer to be 5 and not 6. Similarly for any other years.

Thanks!

Answer 1

One way to do it is the following:

public static int DayDiff(DateTime d1, DateTime d2)
{
    DateTime min, max;
    if(d1 < d2)
    {
        min = d1; max = d2;
    }
    else
    {
        min = d2; max = d1;
    }

    int nbOfDays = 0;
    while(max.Date != min.Date)
    {
        min = min.AddDays(1);
        if (min.Month != 2 || min.Day != 29) // Skip leap day
            nbOfDays++;
    }
    return nbOfDays;
}

Answer 2

This is probably the most complicated way of doing this but it survived my test cases and seems to get the job done.

1. Calculate the difference in total years Years.
2. Compute the Days of the remaining interval.
3. Check it for a leap day. If there is one, compute --Days.
4. Return Days + Years * 365.

/// <summary>
/// Determines the ABSOLUTE difference of FULL years between two dates.
/// Leap days are ignored; the 29th of February is treated as if it was the 28th
/// (conforming with Aventurian calendars).
/// </summary>
/// <param name="Early">The earlier date</param>
/// <param name="Late">The later date</param>
/// <returns>Difference in full years (absolute value >= 0)</returns>
public static int AbsDeltaInYears(DateTime Early, DateTime Late)
{
    if (Early > Late) throw new ArgumentException("'Late' must be greater or equal to 'Early'");

    // Aventurian calendars do not have leap years: check for Feb, 29th
    const int Feb = 2;
    const int LeapDay = 29;
    if (Early.Day == LeapDay && Early.Month == Feb) Early = Early.AddDays(-1);
    if (Late.Day == LeapDay && Late.Month == Feb) Late = Late.AddDays(-1);

    int Delta = Late.Year - Early.Year;

    // correction if the one year is not a full year
    if (Late.Month < Early.Month || (Late.Month == Early.Month && Late.Day < Early.Day))
        Delta--;

    return Delta;
}


/// <summary>
/// Calculate the difference in days (ignoring leap days which the Aventurian calendar does not have).
/// </summary>
/// <param name="time"></param>
/// <param name="reference"></param>
/// <returns></returns>
public static int DeltaInDays(DateTime time, DateTime reference)
{
    // Needed to determine leap years
    GregorianCalendar EarthCalendar = new();

    DateTime Early = time <= reference ? time : reference;
    DateTime Late = time > reference ? time : reference;
    int Years = AbsDeltaInYears(Early, Late);

    // skip leap days by using whole years
    int Days = Years * DaysInYear;
    // add remaining interval
    DateTime EarlyPlusYears = Early.AddYears(Years);
    Days += (Late - EarlyPlusYears).Days;
    // One leap day may be left, remove if necessary
    if (EarthCalendar.IsLeapYear(EarlyPlusYears.Year) && EarlyPlusYears.DayOfYear < 31 + 29)
        Days--;
    else
    {
        if (EarthCalendar.IsLeapYear(Late.Year) && Late.DayOfYear > 31 + 28)
            Days--;
    }
    return Days;
}