This function caluclates dates for the first, second, third, fourth or last occurence of any DayfWeek within a month. A typical application would be to find the date of a UK Bank Holiday. (They often fall on first or last Monday of a month.) I have included some examples demonstrating how to use this function
 

Private Shared Function DayOfWeek_In_Month(WoM As Week_Of_Month, DoW As DayOfWeek, yyyy As Integer, mm As Integer) As Date
 Dim KeyDate As New Date(yyyy, mm, 1, 12, 0, 0, 0, 0)
 Dim WeekStartDate As Date
 Select Case WoM
  Case Week_Of_Month.First : WeekStartDate = New Date(yyyy, mm, 1, 12, 0, 0, 0, 0)
  Case Week_Of_Month.Second : WeekStartDate = New Date(yyyy, mm, 8, 12, 0, 0, 0, 0)
  Case Week_Of_Month.Third : WeekStartDate = New Date(yyyy, mm, 15, 12, 0, 0, 0, 0)
  Case Week_Of_Month.Fourth : WeekStartDate = New Date(yyyy, mm, 22, 12, 0, 0, 0, 0)
  Case Week_Of_Month.Last
   WeekStartDate = New Date(yyyy, mm, Date.DaysInMonth(yyyy, mm) - 6, 12, 0, 0, 0, 0)
   KeyDate = WeekStartDate
 End Select
 Dim AddDays As Integer = (CInt(DoW) + 7 - CInt(KeyDate.DayOfWeek)) Mod 7
 Return WeekStartDate.AddDays(AddDays)
End Function

Public Enum Week_Of_Month
 First
 Second
 Third
 Fourth
 Last
End Enum
  

 
On what date was the FIRST MONDAY in JANUARY 2000 (January is month 1)

   Dim dat As Date = DayOfWeek_In_Month(Week_Of_Month.First, DayOfWeek.Monday, 2000, 1)
  

What date was the LAST SUNDAY in JULY 2021 (July is month 7)

Dim dat As Date = DayOfWeek_In_Month(Week_Of_Month.Last, DayOfWeek.Sunday, 2021, 7)
  

 

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