secret agent coder/decoder ring simulator

[kopzlo]

I really need to know if someone can show me
can I get an example of a program that can

accepts a code number and an input string and outputs a coded version
of the string.

and a second program that
accepts a code number and a scrambled string, and decodes it,
outputting the original sentences

hence both can be put into one program with a menu choice of code or
decode actions.......................thanks