A student writes:

Dr. Patt,

I was curious as to whether or not we need to be able to include in the
input here it is asking the user for either Encryption or Decryption the
capital and lower case values.  In other words, do we have to be able to
account for the fact that the user is able to input a lowercase e or an
uppercase E and likewise for the letter 'D'.  Is it ok to simply include
in the prompt to ask the user to type just lowercase e's or d's or not?
<<name withheld to protect one who wants to give the user a hint>>

Actually, the statement of the assignment states pretty clearly that the
user must type a E or a D, depending on whether to Encrypt or Decrypt,
and our grading script will expect that.  We could make our grading script
more elaborate and cover lower case responses, but I think that is not 
necessary.  I think it is reasonable to expect the user to be able to simply
type an E or D, and if he/she types anything else, the program will not 
encrypt or decrypt.

So, your program should only accept E or D.  


Good luck on completing the assignment.

Yale Patt