C++ Help

Random monoalphabet cipher.

The caeser cipher, which shifts all letters by a certain amount, is easy to decipher. Try this, instead of numbers use letters. Consider this, the word is FEATHER. Remove duplicate letters, making FEATHR, and append the rest of the letters of the alphabet in reverse order.

Now encrypt the letters as follows:

See exhibit A

Now, write a program 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. You must always supply a keyword.