5 REM MICRO ADVENTURE BOOK 2, PROGRAM 1

10 REM ENCODER/DECODER - PAGE 4

15 DIM K$(10), C$(255), P$(255), I$(1)

20 P$ = " "

30 PRINT "ENTER YOUR PASSWORD"

40 INPUT K$

50 PRINT "TYPE EACH LINE OF SECRET MSG"

60 PRINT "(TYPE 'STOP' WHEN DONE)"

70 INPUT C$

80 IF C$ = "STOP" THEN 270
 
90 FOR I = 1 TO LEN(C$)

100 I$ = C$(I,I)

110 IF (I$ >= "A") * (I$ <= "Z") THEN 140

120 P$(LEN(P$)+1) = I$

130 GOTO 230
 
140 J = J + 1

150 IF J <= LEN(K$) THEN 170

160 J = 1

170 K = ASC(K$(J,J)) - ASC("A") + 1

180 C = ASC(I$) - ASC("A") + 1

190 IF K > C THEN 210

200 K = K + 26

210 P = K - C 

220 P$(LEN(P$)+1) = CHR$(P+ASC("A")-1)

230 NEXT I 

240 PRINT P$ 

250 P$ = " " 

260 GOTO 70 

270 END