Using C$++$The Caesar cipher, which shifts all letters by a fixed amount, is far too easy to crack. Here is a better idea. As the key, don$$t use numbers but words. Suppose the key word is FEATHER. Then first remove duplicate letters, yielding FEATHR, and append the other letters of the alphabet in reverse order:

Now encrypt the letters as follows:

Write a program in C$++$that encrypts or decrypts a file using this cipher. For example,

crypt $-$d $-$kFEATHER encrypt.txt output.txt

decrypts a file using the keyword FEATHER. It is an error not to supply a keyword.