Then you'd have to deal with backspace, and the fact that the response may be 999x or 9999x.

What it actually needs is a good generic regular expression udf, so you can do:
code:
While Not $sRoomNumber
   "Enter room number: " GetS $sRoomNumber
   If Not Matches($sRoomNumber,"999[a-e]|9999[a-e]")
      "Room number is invalid." ?
      $sRoomNumber=""
   EndIf
Loop
Oops. Hijacked thread [Embarrassed]