Adding various cells on a click??

assign this code to a button

Public Sub sumcells()
    Dim c As Range
    Dim s
    For Each c In Selection
       If WorksheetFunction.IsNumber(c.Value) Then
         s = s + c.Value
       Else
         s = s & c.Value & " "
       End If
    Next
    Range("G3").Value = s 
    Set c = Nothing
End Sub