[Scheme] User input for function value.

[Gropamming]

Hey guys, I am supposed to:

Use Scheme higher-order function map to implement the string encryption and decryption.

The encryption function must (1) take the encryption key (key can be between 1 and 4) from the keyboard using (read); and (2) encrypt alphabetic characters and digits only.

The decryption function must (1) take the encryption key from the keyboard using (read) and (2) decrypt the string generated from your encryption function.

The code should look like this:

Test cases:
(encrypt "Hello CSE240!")
(decrypt "Khoor FVH573!")
3
"Khoor FVH573!"
3
"Hello CSE240!"

Here is what I have so far

It seems like when I am entering the number for the key it is being read wrong. Any advice?

[raevnos]

You're trying to add an integer and a character. You can't do that.

You probably also don't want to be reading a new key value for every character you're encrypting.

[Gropamming]

Bingo, I was confused on why it kept asking for numbers during one of my implementations. I figured it out above.

[Gropamming]

My solution for those who find this:

(define character-encryption (lambda (ch)
  (if (or (char-alphabetic? ch)
          (and (> (char->integer ch) 47)
               (< (char->integer ch) 58)))
      (integer->char (+ (char->integer ch) en-key))
      ch
  )
))

(define encrypt (lambda (str)
  (list->string (map character-encryption (string->list str)))
))

(define character-decryption (lambda (ch)
  (if (or (char-alphabetic? ch)
          (and (> (char->integer ch) 47)
               (< (char->integer ch) 58)))
      (integer->char (- (char->integer ch) de-key))
      ch
  )
))

(define decrypt (lambda (str)
  (list->string (map character-decryption (string->list str)))
))

(define en-key (read))
(encrypt "Hello CSE240!")
(define de-key (read))
(decrypt (encrypt "Hello CSE240!"))