Alright, seriously drifting off topic, but I thought I'd chime in: there are two varieties of airport codes: ICAO and IATA.
ICAO: Four letters, with rules assigning different letters to specific countries or regions. Also includes "national identifiers" for smaller airports which may be shorter, or contain alphanumeric characters.
IATA: Three letters only.
In some cases, the two codes for a given airport are very similar, e.g. much of the U.S. and Canada: KLAX (ICAO) and LAX (IATA) or CYUL and YUL.
Elsewhere, not so much: CDG and LFPG (Paris - Charles-de-Gaule) or DME and UUDD (Moscow Domedovo).