(define (expt-rec num exp)
  (if (= 0 exp)
      1
      (* num (expt-rec num (- exp 1)))))


(define (expt-iter num exp)
  (define (loop res exp-remaining)
    (if (= 1 exp-remaining)
        res
        (loop (* res num) (- exp-remaining 1))))
  (loop num exp))