Break ON
$gNull=SetOption("Explicit","ON")

Dim $sRoomNumber,$iRoomNumberLen,$sErrorMessage,$sNumberPart

$sErrorMessage="ERROR: Room number must be 3 or 4 digits, followed by a letter a-e e.g. 405b"+@CRLF

While Not $sRoomNumber
        "Enter a room number (e.g. 401e): " GetS $sRoomNumber
        $sRoomNumber=LCase($sRoomNumber)
        $iRoomNumberLen=Len($sRoomNumber)
        Select
        Case $iRoomNumberLen=4 OR $iRoomNumberLen=5
                If Not InStr("abcde",Right($sRoomNumber,1))
                        $sErrorMessage
                        $sRoomNumber=""
                Else
                        $sNumberPart=Left($sRoomNumber,$iRoomNumberLen-1)
                        If Not $sNumberPart=Cstr(Val($sNumberPart))
                                $sErrorMessage
                                $sRoomNumber=""
                        EndIf
                EndIf
        Case "LengthIsInvalid"
                $sErrorMessage
                $sRoomNumber=""
        EndSelect
Loop

"Valid room number entered:" $sRoomNumber ?

Exit 0