Excel vba code understand

sorry If I sound to annoying but I just want to understand it once very clearly because lines like these are used quiet often

Orite.. - now I know and I can simple write the same statement for last occupied cell if I have to - JUST PERFACT

I have another question though,
I am following an example - please have a look at the code below
Its basically to enter values values in excel sheet - database - using a command button

Know I know that we can use 'Exit Function' to exit function
But I am trying to implement the error handling here but not sure
For example it throws the 'alert' when 'partid' is not given but would still write the row - which it shouldn't

It would great if you get me started on it or just quickly edit the code to be able to handle the 'nulls' etc

Thanks

Private Sub cmdAdd_Click()

Dim iRom As Long
Dim ws As Worksheet
Set ws = Worksheets("PartsData")
'find first empty row in the database
iRow = ws.Cells(Rows.Count, 1) _
.End(xlUp).Offset(1, 0).Row

'check for a part number
If Trim(Me.txtPart.Value) = "" Then
Me.txtPart.SetFocus
MsgBox "Please enter part number"
Exit()
End If

'assign the values
ws.Cells(iRow, 1).Value = Me.txtPart.Value
ws.Cells(iRow, 2).Value = Me.txtLocation
ws.Cells(iRow, 3).Value = Me.txtDate
ws.Cells(iRow, 4).Value = Me.txtQuantity

'clear the data
Me.txtPart.Value = ""
Me.txtLocation = ""
Me.txtDate = ""
Me.txtQuantity = ""



End Sub

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how do we convert string to number?

Change line 15 from  "End if" to "Else"

and add "End if" on line 22


To convert string to number the conventional function is
a = val(string)

but quite often this is very conveniently done by

a = --string

or

a = string * 0

thanks