Error Overflow in VBA - excel

Question

I'm a newbie to VBA. Recently, I have typed some codes and following is the sample of my codes:
Dim n As Long
n = Range("A1", Range("A1").End(xlDown)).Rows.Count
For i = 3 To n
Range("P" & i).Value = WorksheetFunction.IfError(Range("N" & i).Value / Range("O" & i).Value, 0))
Next
And it turns out to have the error of Overflow. I have searched on the Internet and figure out it my sample code should be converted to Long type data. However, when I change into:
Range("P" & i).Value = CLng(WorksheetFunction.IfError(CLng(Range("N" & i).Value) / CLng(Range("O" & i).Value), 0))
the problem also remains.
Thank you for any help !

Answer 1

The division in your code (Range("N" & i).Value / Range("O" & i).Value) is happening before it is passed as a parameter to the IfError function. Therefore, if the division fails, your code crashes and the IfError never gets a chance to do anything.
An alternate way of doing this would be:
Dim n As Long
n = Range("A1", Range("A1").End(xlDown)).Rows.Count
For i = 3 To n
'Set the value in column P to a default value
Range("P" & i).Value = 0
'Switch on error handling
On Error Resume Next
'Attempt the calculation - if it fails, the value in column P will not change
Range("P" & i).Value = Range("N" & i).Value / Range("O" & i).Value
'Switch error handling off again
On Error GoTo 0
Next

Answer 2

You can check whether the cell value is zero or null. If not you can perform your caluculation.
Sub Demo()
Dim n As Long
n = Range("A1", Range("A1").End(xlDown)).Rows.Count
For i = 3 To n
If NotNullOrZero(Range("O" & i).Value) Then
Range("P" & i).Value = WorksheetFunction.IfError(Range("N" & i).Value / Range("O" & i).Value, 0)
Else
Range("P" & i).Value = ""
End If
Next
End Sub
Public Function NotNullOrZero(aValue As Variant) As Boolean
' Returns true if the value is not null and greater than zero
If Not IsNull(aValue) Then
If (aValue > 0) Then
NotNullOrZero = True
End If
End If
NotNullOrZero = False
End Function
Got NotNullOrZero function from here answered by #BrianKE.