Question

How can I get the start and end date of a given year (int), given month (int), and given week (int) { example Year : 2011 Month: 07 week: 04 } in c# 4.0? Thanks in advance.

The Start Date of the Year 2011 Month 07 and the week number of the month is 04.

Answer 1

Google is your friend.

Months:

public DateTime FirstDayOfMonthFromDateTime(DateTime dateTime)
{
   return new DateTime(dateTime.Year, dateTime.Month, 1);
}


public DateTime LastDayOfMonthFromDateTime(DateTime dateTime)
{
   DateTime firstDayOfTheMonth = new DateTime(dateTime.Year, dateTime.Month, 1);
   return firstDayOfTheMonth.AddMonths(1).AddDays(-1);
}

You can do something similar for years:

   DateTime time = new DateTime(2011,1,1);
   time.AddYears(1).AddDays(-1);

And week needs to use the CultureInfo.FirstDay (or whatever you want to set as the first day of a week, in some countries it’s Monday, sometimes it’s Sunday).

/// <summary>
    /// Returns the first day of the week that the specified
    /// date is in using the current culture. 
    /// </summary>
    public static DateTime GetFirstDayOfWeek(DateTime dayInWeek)
    {
        CultureInfo defaultCultureInfo = CultureInfo.CurrentCulture;
        return GetFirstDateOfWeek(dayInWeek, defaultCultureInfo);
    }

    /// <summary>
    /// Returns the first day of the week that the specified date 
    /// is in. 
    /// </summary>
    public static DateTime GetFirstDayOfWeek(DateTime dayInWeek, CultureInfo cultureInfo)
    {
        DayOfWeek firstDay = cultureInfo.DateTimeFormat.FirstDayOfWeek;
        DateTime firstDayInWeek = dayInWeek.Date;
        while (firstDayInWeek.DayOfWeek != firstDay)
            firstDayInWeek = firstDayInWeek.AddDays(-1);

        return firstDayInWeek;
    }