Premier lundi du mois en cours dans VBA

Vous pouvez utiliser cette fonction générique:

' Calculates the date of the occurrence of Weekday in the month of DateInMonth.
'
' If Occurrence is 0 or negative, the first occurrence of Weekday in the month is assumed.
' If Occurrence is 5 or larger, the last occurrence of Weekday in the month is assumed.
'
' If Weekday is invalid or not specified, the weekday of DateInMonth is used.
'
' 2016-06-09. Gustav Brock, Cactus Data ApS, CPH.
'
Public Function DateWeekdayInMonth( _
    ByVal DateInMonth As Date, _
    Optional ByVal Occurrence As Integer, _
    Optional ByVal Weekday As VbDayOfWeek = -1) _
    As Date

    Const DaysInWeek    As Integer = 7

    Dim Offset          As Integer
    Dim Month           As Integer
    Dim Year            As Integer
    Dim ResultDate      As Date

    ' Validate Weekday.
    Select Case Weekday
        Case _
            vbMonday, _
            vbTuesday, _
            vbWednesday, _
            vbThursday, _
            vbFriday, _
            vbSaturday, _
            vbSunday
        Case Else
            ' Zero, none or invalid value for VbDayOfWeek.
            Weekday = VBA.Weekday(DateInMonth)
    End Select

    ' Validate Occurence.
    If Occurrence <= 0 Then
        Occurrence = 1
    ElseIf Occurrence > 5 Then
        Occurrence = 5
    End If

    ' Start date.
    Month = VBA.Month(DateInMonth)
    Year = VBA.Year(DateInMonth)
    ResultDate = DateSerial(Year, Month, 1)

    ' Find offset of Weekday from first day of month.
    Offset = DaysInWeek * (Occurrence - 1) + (Weekday - VBA.Weekday(ResultDate) + DaysInWeek) Mod DaysInWeek
    ' Calculate result date.
    ResultDate = DateAdd("d", Offset, ResultDate)

    If Occurrence = 5 Then
        ' The latest occurrency of Weekday is requested.
        ' Check if there really is a fifth occurrence of Weekday in this month.
        If VBA.Month(ResultDate) <> Month Then
            ' There are only four occurrencies of Weekday in this month.
            ' Return the fourth as the latest.
            ResultDate = DateAdd("d", -DaysInWeek, ResultDate)
        End If
    End If

    DateWeekdayInMonth = ResultDate

End Function

Alors:

FirstMonday = DateWeekdayInMonth(Date, 1, vbMonday)

Exécutez la macro suivante et elle vous donne le premier lundi du mois:

Sub PromptFirstMondayofTheCurrentMonth()

Dim a As Variant

a = Date - Day(Date) + 1

MsgBox IIf(Weekday(a, vbMonday) = 1, 1, 9 - Weekday(a, vbMonday))

End Sub