REM Program to help solve "CryptoQuip" newspaper puzzle
10 DIM a, b, c, d, e, f
20 DIM key$, quip$, out1$, out2$, out3$, out4$, oldlet$, med1$, med2$
30 CLS : LOCATE 5, 1: LINE INPUT "Enter the CryptoQuip: "; quip$
40 quip$ = UCASE$(quip$): a = LEN(quip$): b = INT(a / 2): c = 0: d = 1
43 IF b + c <= a THEN
     e = ASC(MID$(quip$, (b + c), 1))
     IF ((e < 65) OR (e > 96)) THEN GOTO 46
     IF d = 1 THEN c = ABS(c) + 1: d = 0 ELSE c = -c: d = 1
     GOTO 43
   END IF
46 b = b + c: c = a - b: d = 0
50 e = 1: out1$ = LEFT$(quip$, b): out2$ = MID$(quip$, (b + 1))
60 CLS : LOCATE 5, 1:
   PRINT "Move cursor with arrows; type a replacement letter; ESC when done."
70 LOCATE 7, 1: PRINT out1$: LOCATE 10, 1: PRINT out2$
80 out3$ = out1$
   FOR a = 1 TO b: f = ASC(MID$(out3$, a, 1))
     IF ((f > 64) AND (f < 97)) THEN MID$(out3$, a, 1) = " "
   NEXT
85 out4$ = out2$
   FOR a = 1 TO c: f = ASC(MID$(out4$, a, 1))
     IF ((f > 64) AND (f < 97)) THEN MID$(out4$, a, 1) = " "
   NEXT
90 f = 1: LOCATE 8, 1: PRINT out3$: LOCATE 11, 1: PRINT out4$: GOTO 100
91  LOCATE 13, 1: PRINT "Legal Keys are Cursor, Alphabet, Space": GOTO 100
92  LOCATE 13, 1: PRINT "Key Is Same As Crypto Letter          ": GOTO 100
93  LOCATE 13, 1: PRINT "Only Crypto Letters Can Be Changed    ": GOTO 100
94  LOCATE 13, 1: PRINT "Key Already Assigned To Crypto Letter "
100 LOCATE 7 + d, ((1 - (d / 3)) * e + ((d / 3) * f)), 1, 25, 31
    key$ = INKEY$: a = LEN(key$)
    IF a = 0 THEN GOTO 100
110 LOCATE 13, 1: PRINT "                                      "
    IF key$ = CHR$(27) THEN
      LOCATE 20, 1
      INPUT "Are you SURE you want to quit (Y/N)?"; key$
      IF ((key$ = "y") OR (key$ = "Y")) THEN SYSTEM
      LOCATE 20, 1: PRINT STRING$(60, " "): GOTO 100
    END IF
120 IF a = 2 THEN
      a = INSTR("HKMP", RIGHT$(key$, 1))
      IF a = 0 THEN GOTO 91
      IF a = 1 THEN d = 0: GOTO 100
      IF a = 4 THEN d = 3: GOTO 100
      IF a = 2 THEN
        IF d = 0 THEN
          IF e = 1 THEN GOTO 100 ELSE e = e - 1: GOTO 100
        ELSE
          IF f = 1 THEN GOTO 100 ELSE f = f - 1: GOTO 100
        END IF
      END IF
      IF a = 3 THEN
        IF d = 0 THEN
          IF e = b THEN GOTO 100 ELSE e = e + 1: GOTO 100
        ELSE
          IF f = c THEN GOTO 100 ELSE f = f + 1: GOTO 100
        END IF
      END IF
    END IF
130 key$ = UCASE$(key$): a = ASC(key$)
      IF ((a < 65) OR (a > 96)) THEN IF a <> 32 THEN GOTO 91
140 IF d = 0 THEN oldlet$ = MID$(out1$, e, 1) ELSE oldlet$ = MID$(out2$, f, 1)
150 IF oldlet$ = key$ THEN IF key$ = " " THEN GOTO 100 ELSE GOTO 92
160 a = ASC(oldlet$): IF ((a < 65) OR (a > 96)) THEN GOTO 93
170 a = INSTR(out3$, key$): IF ((a > 0) AND (key$ <> " ")) THEN GOTO 94
    a = INSTR(out4$, key$): IF ((a > 0) AND (key$ <> " ")) THEN GOTO 94

200 med1$ = out1$: med2$ = out2$
210 a = INSTR(med1$, oldlet$)
    IF a > 0 THEN
      MID$(med1$, a, 1) = " "
      MID$(out3$, a, 1) = key$
      GOTO 210
    END IF
220 a = INSTR(med2$, oldlet$)
    IF a > 0 THEN
      MID$(med2$, a, 1) = " "
      MID$(out4$, a, 1) = key$
      GOTO 220
    END IF
230 LOCATE 8, 1: PRINT out3$: LOCATE 11, 1: PRINT out4$: GOTO 100