Common Lisp let function

I'm just starting to program in Common Lisp and going back through programs that I coded during some of my previous classes to learn and I am having trouble understanding the problem in my code.

(defun input-1 ()
       (defvar *message* (read-line))
       (defvar *a-value* (parse-integer(read-line)))
       (defvar *b-value* (parse-integer(read-line))))

(defun alphabet (list " " "a" "b" "c" "d" "e" "f" "g" "h" "i" "j" "k" "l" "m"
         "n" "o" "p" "q" "r" "s" "t" "u" "v" "w" "x" "y" "z"))

(defun alphabet-num (list 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
             20 21 22 23 24 25 26 27 28 29))
;(defun inverse (value)
;  (let ((x 0))
;    (loop while (< x 29)
;    (print x))))

(defun inverse (value)
       (dotimes (x 28)
           (when (equal (mod (* x value) 29) 1)
             (return-from inverse x))))

(defun get-int (string)
  (getf (position string alphabet) alphabet-num))

(defun get-string (int)
  (getf (position int alphabet) alphabet))

(defun cipher-calc (character)
  (let ((c-int (get-int character))
    (f-char ""))
    (setf c-int (* *a-value* (- c-int *b-value*)))
    (setf f-char (get-string (mod (abs c-int) 29)))))

However, I am getting this error

; in: DEFUN CIPHER-CALC
;     (* *A-VALUE* (- C-INT *B-VALUE*))
; 
; caught WARNING:
;   undefined variable: *A-VALUE*

;     (- C-INT *B-VALUE*)
; 
; caught WARNING:
;   undefined variable: *B-VALUE*

;     (GET-INT CHARACTER)
; 
; caught STYLE-WARNING:
;   undefined function: GET-INT

;     (GET-STRING (MOD (ABS C-INT) 29))
; 
; caught STYLE-WARNING:
;   undefined function: GET-STRING
; 
; compilation unit finished
;   Undefined functions:
;     GET-INT GET-STRING
;   Undefined variables:
;     *A-VALUE* *B-VALUE*
;   caught 2 WARNING conditions
;   caught 2 STYLE-WARNING conditions

I find it difficult to believe that you cannot call a function inside of a let block, so I'm assuming I am making an error. Any other tips on my code would be welcome.

Solution

Your code:

(defun input-1 ()
  (defvar *message* (read-line))
  (defvar *a-value* (parse-integer(read-line)))
  (defvar *b-value* (parse-integer(read-line))))

DEFVAR is supposed to be used on the top-level and not inside a function. In this case the variables will be defined when the function runs. But when you just compile, evaluate or load such a function, the variable is not defined. Thus the compiler will later warn that in your code these variables are undefined.

When DEFVAR is used at top-level, then Lisp will recognize that there are variable definitions.

(defvar *message*)
(defvar *a-value*)
(defvar *b-value*))

(defun input-1 ()
  (setf *message* (read-line))
  (setf *a-value* (parse-integer (read-line)))
  (setf *b-value* (parse-integer (read-line))))