Can You do this program?

Question

I need a program able to decodify letters and another to codify, so if you input for example: "B" (in the first program) the ouput should be: "A" and viceversa for the second program, also the programs should be able to put a great amount of text and depending the program You should be able to codify or decodify all the text (letter per letter). Is it possible?

Answer 1

Yes.

Answer 2

One of the users I've seen (so there could be many more) has even done conversions from binary and back. Similar idea.

Answer 3

Xdr. -1