10 REM Caesar cipher
20 CLS
30 DEC$ = ""
40 TYPE$ = "cleartext "
50 PRINT "If decrypting enter  "+"<d> "+" -- else press enter "; : INPUT DEC$
60 INPUT "Enter offset > "; IOFFSET
70 IF DEC$ = "d" THEN IOFFSET = 26-IOFFSET: TYPE$ = "ciphertext "
110 PRINT "Enter "+TYPE$+"> ";
120 INPUT CAD$
140 LONGITUD = LEN(CAD$)
150 FOR I = 1 TO LONGITUD
160   ITEMP = ASC(MID$(CAD$,I,1))
170   IF ITEMP > 64 AND ITEMP < 91 THEN ITEMP = ((ITEMP-65)+IOFFSET) MOD 26 :  PRINT CHR$(ITEMP+65); : ELSE PRINT CHR$(ITEMP);
230 NEXT I
240 PRINT
250 END