(defun te (n)
  (interactive "p")
  (elt ["a" "b" "D"] n))

(defun te2 (n)
  (interactive "p")
  (message (elt ["a" "b" "D"] n)))

(te 1)   ;; no output if using prefix argument
(te2 1)  ;; value of eval is not "b" but b if useing prefix argument