Challenge: Validate a code

[Meg]

How's this for cramming the codes into as little memory as possible? No arrays (this outta be good for a laugh, at least!)

Code:

DECLARE FUNCTION GetCode& ()

CLS
SCREEN 11

OPEN "VALID.TXT" FOR INPUT AS #1
     FOR i% = 1 TO 20000
          INPUT #1, n&
          PSET (n& MOD 640, n& \ 640), 15
     NEXT i%
CLOSE #1

DO
     UserCode& = GetCode&
     PRINT UserCode&; "is ";
     IF POINT(UserCode& MOD 640, UserCode& \ 640) THEN
          PRINT "Valid.              "
     ELSE
          PRINT "Invalid.            "
     END IF
LOOP

FUNCTION GetCode&
    
     LOCATE 12, 1: PRINT SPC(79);
     LOCATE 12, 1: PRINT "Enter Code: ";

     Code& = 0
     DO
          LOCATE 12, 13: PRINT Code&; " "
          DO
               c$ = INKEY$
          LOOP UNTIL c$ <> ""
          IF c$ = CHR$(27) THEN SYSTEM
          IF c$ = CHR$(13) THEN EXIT DO
          IF c$ = CHR$(8) THEN Code& = Code& \ 10
          IF c$ >= "0" AND c$ <= "9" THEN
               IF Code& <= 9999 THEN Code& = Code& * 10 + VAL(c$)
          END IF
     LOOP

     GetCode& = Code&

END FUNCTION

*peace*

Meg.