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
80   ioffset = 26-ioffset
90   type$ = "ciphertext "
100 endif
110 print "Enter "+type$+"> ";
120 input cad$
130 cad$ = ucase$(cad$)
140 longitud = len(cad$)
150 for i = 1 to longitud
160   itemp = asc(mid$(cad$,i,1))
170   if itemp > 64 and itemp < 91 then
180     itemp = ((itemp-65)+ioffset) mod 26
190     print chr$(itemp+65);
200   else
210     print chr$(itemp);
220   endif
230 next i
240 print
250 end