Source Code
10 REM "CYPHER"
40 FAST
50 DIM A(26,26)
60 LET J=-1
70 FOR I=1 TO 26
80 LET J=J+1
90 FOR K=1 TO 26
100 LET A(I,K)=K+J
110 IF A(I,K)>26 THEN LET A(I,K)=A(I,K)-26
120 NEXT K
130 NEXT I
150 PRINT
160 PRINT
170 SLOW
180 PRINT " ENTER KEYWORD"
190 INPUT K$
200 PRINT K$
210 PRINT
220 PRINT " ENTER MESSAGE"
230 INPUT M$
240 PRINT M$
250 PRINT
260 PRINT " ENCYPHER/DECYPHER? (ENTER E OR D)"
270 INPUT Q$
280 PRINT
290 IF Q$="E" THEN GOTO 320
300 IF Q$="D" THEN GOTO 440
310 IF Q$<>"E" OR Q$<>"D" THEN GOTO 260
330 FAST
340 PRINT " ENCYPHERED MESSAGE READS:-"
350 PRINT
360 LET S=0
370 LET T=0
380 LET S=S+1
390 IF S>LEN K$ THEN LET S=S-LEN K$
400 LET T=T+1
410 PRINT CHR$ (37+A(CODE K$(S)-37,CODE M$(T)-37));
420 IF T=LEN M$ THEN GOTO 140
430 GOTO 380
450 FAST
460 LET Z=0
470 PRINT " DECYPHERED MESSAGE READS:-"
480 PRINT
490 FOR W=1 TO LEN M$
500 LET Z=Z+1
510 IF Z>LEN K$ THEN LET Z=Z-LEN K$
520 FOR X=1 TO 26
530 IF A(CODE K$(Z)-37,X)=CODE M$(W)-37 THEN PRINT CHR$ (X+37);
540 NEXT X
550 NEXT W
560 GOTO 140
570 SAVE "1017%7"
580 RUN
