Try
'Code that may raise an error.
Catch
'Code to handle the error.
Finally
'Code to do any final clean up.
End Try
--------->>
Try
vysledek.Text = 2 * 3,141592 * polomer.Text
Catch
MsgBox "Lucinka nikdy nezadava znaky misto cislic"
Finally
/nic/prazdno/dokonceni
End Try
Podle google...