Get the start and end date of a given week year, given month & given week

How can I get the start and end date of a given year (int),开发者_高级运维 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.

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;
    }

Not sure, but is this what you're after?

var weekStart = new DateTime(year, month, 1).AddDays(week * 7);
var weekEnd = weekStart.AddDays(6);

Assuming you start with week 1:

var startDate = new DateTime(year, month, 1).AddDays((week - 1) * 7);
var endDate = startDate.AddDays(6);

You could also use

DateTime.DaysInMonth(int year,int month);

to figure it out. The weeks will be more difficult.

DateTime calculations as these are a bit tricky, with some assumptions i could come up with this

//assign it to the first day of the month
DateTime getweek = new DateTime(2011, 4, 1);
// say the week starts on a Sunday
while (getweek.DayOfWeek != DayOfWeek.Sunday)
      getweek = getweek.AddDays(1);
DateTimeFormatInfo info = DateTimeFormatInfo.CurrentInfo;            
Calendar cal = info.Calendar;
//Now you are on the first week add 3 more to move to the Fourth week
DateTime start = cal.AddWeeks(getweek, 3); // 24 April 2011
DateTime end = start.AddDays(6); // 30 April 2011