help with Code modification

I have the following code that I would like to modify so where it says (result "pass") I would like to see the result of C1+D1 in value So it never changes again.
I need to repeat this from cell A1 to cell A500

Can it be done?

Thank you

Private Sub Worksheet_SelectionChange(ByVal Target As Range)

Dim score As Integer, result As String
A1 = Range("A1").Value

If A1 > 0 Then
    result = "Pass"
End If

Range("B1").Value = result

End Sub