macro to check non blank cells in a column to ensure isdate() - vba

Question

I've been looking to write a macro to check 3 columns to ensure the contents are a date value. The columns can contain empty cells.
The below returns a message box for each cell that is not a date, even the blanks.
Sub DateCheck()
With ActiveSheet
lastRow = .Range("AB" & Rows.Count).End(xlUp).Row
For RowCount = 2 To lastRow
POC = .Range("AB" & RowCount)
If Not IsDate(POC) Then
MsgBox ("Please enter valid date in Cell : AB" & RowCount & ". Example: dd/mm/yyyy")
End If
Next RowCount
End With
End Sub
Could anybody be so kind as to help to adjust this to look at 3 non-adjacent columns, ignore blank cells and only return one message per column in the event it finds non-date values?
Thanks as always
Chris

Answer 1

Code:
Sub DateCheck()
Dim s(2) As String
Dim i As Integer
Dim o As String
Dim lastRow As Long
Dim r As Long
'Enter columns here:
s(0) = "A"
s(1) = "B"
s(2) = "C"
For i = 0 To 2
With ActiveSheet
lastRow = .Range(s(i) & Rows.Count).End(xlUp).Row
For r = 2 To lastRow
POC = .Range(s(i) & r)
If Not IsDate(POC) Then
o = o & ", " & .Range(s(i) & r).Address
End If
Next r
MsgBox ("Please enter valid date in Cells : " & Right(o, Len(o) - 1) & ". Example: dd/mm/yyyy")
o = ""
End With
Next i
End Sub

Answer 2

I would change your loop to a For Each In ... Next and use .Union to construct a range of non-adjacent columns.
Sub MultiDateCheck()
Dim lr As Long, cl As Range, rng As Range, mssg As String
With ActiveSheet
lr = .Range("AB" & Rows.Count).End(xlUp).Row
Set rng = Union(.Range("AB2:AB" & lr), .Range("AM2:AM" & lr), .Range("AZ2:AZ" & lr))
For Each cl In rng
If Not IsDate(cl.Value) And Not IsEmpty(cl) Then _
mssg = mssg & cl.Address(0, 0) & Space(4)
Next cl
End With
If CBool(Len(mssg)) Then
MsgBox ("Please enter valid date(s) in Cell(s): " & Chr(10) & Chr(10) & _
mssg & Chr(10) & Chr(10) & _
"Example: dd/mm/yyyy")
Else
MsgBox "All dates completed!"
End If
Set rng = Nothing
End Sub
I've used a single lastrow from column AB to determined the scope of the cells to be examined but individual rows for each column could easily be compensated for.
Addendum: Code modified for a single message showing rogue non-date/non-blank cells (as below). The Chr(10) is simply a line feed character.