Question

I have seen numerous posts related to adding working days (excluding weekends) to a date parameter and I tried using a few from those. However, all the solutions I picked are failing in some scenarios.
below is the code I’m currently using:

private DateTime AddWorkingDays(DateTime dateValue, int noOfDays) 
    {
        // determine if we are adding or subtracting the days
        int nDirection = noOfDays < 0 ? -1 : 1;

        // move ahead the day of week
        int nWeekday = noOfDays % 5;
        while (nWeekday != 0)
        {
            dateValue = dateValue.AddDays(nDirection);
            if (dateValue.DayOfWeek != DayOfWeek.Saturday
                && dateValue.DayOfWeek != DayOfWeek.Sunday)
            {
                nWeekday -= nDirection;
            }
        }

        // move ahead the number of weeks
        int nDayweek = (noOfDays / 5) * 7;
        dateValue = dateValue.AddDays(nDayweek);

        return dateValue;
    } 

Example scenarios that fail:
Date: 24 Nov, 2012(saturday), No of days: 5 (or 10)
Result: 1 Dec, 2012 (or 8 Dec, 2012) when the expected result was 30 Nov, 2012
Fails for 25 Nov, 2012 also.. and similar scenarios I guess, where the input date falls on a weekend.

Can someone please help fixing such scenarios ? Or provide a better solution ?

Thank you

Answer 1

This implementation (actually quite similar to yours) gives the results you expect:

    public static DateTime AddWorkingDays(this DateTime date, int days)
    {
        if (days == 0)
            return date;
        int sign = days < 0 ? -1 : 1;
        while (days % 5 != 0 || !date.IsWorkingDay())
        {
            date = date.AddDays(sign);
            if (!date.IsWorkingDay())
                continue;
            days -= sign;
        }
        int nWeekEnds = days / 5;
        DateTime result = date.AddDays(days + nWeekEnds * 2);
        return result;
    }

    public static bool IsWorkingDay(this DateTime date)
    {
        return !(date.DayOfWeek == DayOfWeek.Saturday || date.DayOfWeek == DayOfWeek.Sunday);
    }