Visual Basic

<br />
    Private Function  Weeknumber_Entire4DayWeekRule(ByVal inDate As  DateTime) As Integer<br />
        Const JAN As Integer = 1<br />
        Const DEC As Integer = 12<br />
        Const LASTDAYOFDEC As Integer = 31<br />
        Const FIRSTDAYOFJAN As Integer = 1<br />
        Const THURSDAY As Integer = 4<br />
        Dim ThursdayFlag As Boolean = False<br />
<br />
        ' Get the day number since the beginning of the year<br />
        Dim DayOfYear As Integer = inDate.DayOfYear<br />
<br />
        ' Get the numeric weekday of the first day of the<br />
        ' year (using sunday as FirstDay)<br />
        Dim StartWeekDayOfYear As Integer = _<br />
           DirectCast(New DateTime(inDate.Year, JAN, FIRSTDAYOFJAN).DayOfWeek, Integer)<br />
        Dim EndWeekDayOfYear As Integer = _<br />
            DirectCast(New DateTime(inDate.Year, DEC, LASTDAYOFDEC).DayOfWeek, Integer)<br />
<br />
        ' Compensate for the fact that we are using monday<br />
        ' as the first day of the week<br />
        If StartWeekDayOfYear = 0 Then<br />
            StartWeekDayOfYear = 7<br />
        End If<br />
        If EndWeekDayOfYear = 0 Then<br />
            EndWeekDayOfYear = 7<br />
        End If<br />
<br />
        ' Calculate the number of days in the first and last week<br />
        Dim DaysInFirstWeek As Integer = 8 - StartWeekDayOfYear<br />
        Dim DaysInLastWeek As Integer = 8 - EndWeekDayOfYear<br />
<br />
       ' If the year either starts or ends on a thursday it will have a 53rd week<br />
        If StartWeekDayOfYear = THURSDAY OrElse EndWeekDayOfYear = THURSDAY Then<br />
            ThursdayFlag = True<br />
       End If<br />
<br />
        ' We begin by calculating the number of FULL weeks between the start of the year and<br />
        ' our date. The number is rounded up, so the smallest possible value is 0.<br />
        Dim FullWeeks As Integer = _<br />
            CType(Math.Ceiling((DayOfYear - DaysInFirstWeek) / 7), Integer)<br />
 <br />
        Dim WeekNumber As Integer = FullWeeks<br />
<br />
        ' If the first week of the year has at least four days, then the actual week number for our date<br />
        ' can be incremented by one.<br />
       If DaysInFirstWeek >= THURSDAY Then<br />
            WeekNumber = WeekNumber + 1<br />
        End If<br />
<br />
       ' If week number is larger than week 52 (and the year doesn't either start or end on a thursday)<br />
        ' then the correct week number is 1.<br />
       If WeekNumber > 52 AndAlso Not ThursdayFlag Then<br />
            WeekNumber = 1<br />
        End If<br />
<br />
        'If week number is still 0, it means that we are trying to evaluate the week number for a<br />
        'week that belongs in the previous year (since that week has 3 days or less in our date's year).<br />
        'We therefore make a recursive call using the last day of the previous year.<br />
        If WeekNumber = 0 Then<br />
            WeekNumber = Weeknumber_Entire4DayWeekRule( _<br />
                New DateTime(inDate.Year - 1, DEC, LASTDAYOFDEC))<br />
        End If<br />
        Return WeekNumber<br />
    End Function

ChandraRam wrote:

I am not aware of any direct function call