Jag vill att man från årtal och datum ska kunna få fram vilken vecka det är.

Är det nån som vet hur man gör?

tack på förhand

I vb6 använde jag mig av denna koden. Kanske fungerar i .NET också

Public Function WeekNumber(InDate As Date) As Integer
    Dim DayNo As Integer
    Dim StartDays As Integer
    Dim StopDays As Integer
    Dim StartDay As Integer
    Dim StopDay As Integer
    Dim VNumber As Integer
    Dim ThurFlag As Boolean
    
    DayNo = Days(InDate)
    StartDay = Weekday(DateSerial(Year(InDate), 1, 1)) - 1
    StopDay = Weekday(DateSerial(Year(InDate), 12, 31)) - 1
    ' Number of days belonging to first calendar week
    StartDays = 7 - (StartDay - 1)
    ' Number of days belonging to last calendar week
    StopDays = 7 - (StopDay - 1)
    
    ' Test to see if the year will have 53 weeks or not
    If StartDay = 4 Or StopDay = 4 Then ThurFlag = True Else ThurFlag = False
    
    VNumber = (DayNo - StartDays - 4) / 7
    ' If first week has 4 or more days, it will be calendar week 1
    ' If first week has less than 4 days, it will belong to last year's
    ' last calendar week
    If StartDays >= 4 Then
        WeekNumber = Fix(VNumber) + 2
    Else
        WeekNumber = Fix(VNumber) + 1
    End If
    
    ' Handle years whose last days will belong to coming year's first
    ' calendar week
    If WeekNumber > 52 And ThurFlag = False Then WeekNumber = 1
    ' Handle years whose first days will belong to the last year's
    ' last calendar week
    
    If WeekNumber = 0 Then
        WeekNumber = WeekNumber(DateSerial(Year(InDate) - 1, 12, 31))
    End If
    
End Function

[Problem med "vecko-nummer" i min kalender]