Creates a simple substitution cypher that you define.
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5 REM "CRYPTO"
10 FOR i=65528 TO 65534
12 POKE i,0
14 NEXT i
16 CLS : POKE 23609,30: POKE 65535,128: POKE 23658,8
20 PRINT AT 9,8;"""CRYPTO"" PAD": PRINT : PRINT : PRINT : PRINT
22 PRINT " A SIMPLE-SUBSTITUTION Cipher Scratchpad": PRINT : PRINT : PRINT
24 PRINT " Enter Message or Cryptogram-"
30 LET c$="ABCDEFGHIJKLMNOPQRSTUVWXYZ"
50 INPUT LINE a$
55 LET a$=a$+"\u "
60 CLS
70 PRINT
100 FOR i=33 TO 1 STEP -1
110 IF i>LEN a$ THEN LET i=LEN a$
120 IF a$(i)=" " THEN GO TO 200
130 NEXT i
150 LET r$=a$( TO 32): LET a$=a$(33 TO ): GO TO 300
200 LET r$=a$( TO i-1)
210 LET a$=a$(i+1 TO )
300 PRINT r$
320 PRINT : PRINT
325 IF LEN a$=0 THEN GO TO 360
330 IF a$(1)<>" " THEN GO TO 100
340 LET a$=a$(2 TO )
350 GO TO 330
360 PRINT AT 21,0; FLASH 1;"SETTING PUNCTUATION"
365 FOR r=1 TO 20 STEP 3
370 FOR c=0 TO 31
375 LET p=CODE SCREEN$ (r,c)
380 IF p=0 THEN GO TO 480
385 IF p=32 THEN GO TO 395
390 IF (p<65 OR p>90) THEN PRINT AT r+1,c;SCREEN$ (r,c)
395 NEXT c
396 NEXT r
480 PRINT AT 21,0;"LET "; FLASH 1;"?"; FLASH 0;"=";c$
490 LET h=0
495 BEEP .03,20
500 IF INKEY$<>"" THEN GO TO 500
501 IF INKEY$="" THEN GO TO 501
502 LET l$=INKEY$
504 IF l$>"`" OR l$<" " THEN GO TO 500
505 BEEP .02,15
510 PRINT AT 21,4;l$
515 FOR r=1 TO 20 STEP 3
520 FOR c=0 TO 31
530 IF SCREEN$ (r,c)=l$ THEN PRINT AT r,c; FLASH 1;l$: BEEP .03,30: LET h=1
540 IF CODE SCREEN$ (r,c)=0 THEN GO TO 595
550 NEXT c
590 NEXT r
595 BEEP .01,10
600 IF NOT h THEN GO TO 480
605 INPUT "Substitute which letter?";m$
610 IF m$="" THEN GO TO 605
612 LET m$=m$(1)
613 IF m$<" " OR m$>"`" THEN GO TO 605
615 IF NOT (m$>"@" AND CODE m$<91) THEN GO TO 650
618 IF c$(CODE m$-64)=" " THEN GO TO 605
630 LET c$(CODE m$-64)=" "
650 FOR r=1 TO 20 STEP 3
655 FOR c=0 TO 31
660 IF SCREEN$ (r,c)<>l$ THEN GO TO 670
662 PRINT AT r,c; FLASH 0;l$
664 LET n$=SCREEN$ (r+1,c)
666 IF (n$>"@" AND CODE n$<91) THEN LET c$(CODE n$-64)=n$
668 PRINT AT r+1,c;m$: BEEP .01,27
670 IF CODE SCREEN$ (r,c)=0 THEN GO TO 480
680 NEXT c
690 NEXT r
9000 SAVE "CRYPTO" LINE 10