How to find the 3rd Friday in a month with C#?

Question

Given a date (of type DateTime), how do I find the 3rd Friday in the month of that date?

Answer 1

I pass this the DateTime for the start of the month I am looking at.

    private DateTime thirdSunday(DateTime timeFrom)
    {
        List<DateTime> days = new List<DateTime>();
        DateTime testDate = timeFrom;

        while (testDate < timeFrom.AddMonths(1))
        {
            if (testDate.DayOfWeek == DayOfWeek.Friday)
            {
                days.Add(testDate);
            }
            testDate = testDate.AddDays(1);
        }

        return days[2];
    }

Answer 2

I'm going to repeat my answer from here with one little addition.

The language-agnostic version:

To get the first particular day of the month, start with the first day of the month: yyyy-mm-01. Use whatever function is available to give a number corresponding to the day of the week; in C# this would be DateTime.DayOfWeek. Subtract that number from the day you are looking for; for example, if the first day of the month is Wednesday (3) and you're looking for Friday (5), subtract 3 from 5, leaving 2. If the answer is negative, add 7. Finally add that to the first of the month; for my example, the first Friday would be the 3rd.

To get the last Friday of the month, find the first Friday of the next month and subtract 7 days.

To get the 3rd Friday of the month, add 14 days to the first Friday.

Answer 3

    int numday = 0;
    int dayofweek = 5; //friday
    DateTime thirdfriday;
    for (int i = 0; i < (date.AddMonths(1) - date).Days && numday <3; i++)
    {
        if ((int)date.AddDays(i).DayOfWeek == dayofweek)
        {
            numday++;
        }
        if (numday == 3)
        {
            thirdfriday = date.AddDays(i);
        }

    }

Answer 4

This is a version that uses LINQ and functional programming style.

It works like this.

First, take all of the days of the month. Then select only the ones of the right day (Friday). Finally take the nth (3rd) entry and return.

// dt: The date to start from (usually DateTime.Now)
// n: The nth occurance (3rd)
// weekday: the day of the week to look for
    public DateTime GetNthWeekdayOfMonth(DateTime dt, int n, DayOfWeek weekday)
    {
        var days = Enumerable.Range(1, DateTime.DaysInMonth(dt.Year, dt.Month)).Select(day => new DateTime(dt.Year, dt.Month, day));

        var weekdays = from day in days
                            where day.DayOfWeek == weekday
                            orderby day.Day ascending
                            select day;

        int index = n - 1;

        if (index >= 0 && index < weekdays.Count())
            return weekdays.ElementAt(index);

        else
            throw new InvalidOperationException("The specified day does not exist in this month!");
   }

Answer 5

I know of no clean/built in way of doing this. But it's not too hard to code up:

        DateTime now = DateTime.Now;

        for (int i = 0; i < 7; ++i)
        {
            DateTime d = new DateTime(now.Year, now.Month, i+1);
            if (d.DayOfWeek == DayOfWeek.Friday)
            {
                return d.AddDays(14);
            }
        }

Answer 6

    public static bool IsThirdWednesday(DateTime inputDate)
    {
        DateTime firstDayOfMonth = new DateTime(inputDate.Year, inputDate.Month, 1);
        DateTime firstDayOfNextMonth = firstDayOfMonth.AddMonths(1);

        int wednesdayCount = 0;
        while(firstDayOfMonth < firstDayOfNextMonth)
        {
            if (firstDayOfMonth.DayOfWeek == DayOfWeek.Wednesday)
                wednesdayCount++;

            if (wednesdayCount == 3)
            {
                if (inputDate == firstDayOfMonth)
                    return true;
                else
                    return false;
              
            }

            firstDayOfMonth = firstDayOfMonth.AddDays(1);
        }

        return false;
    }