Answer Key For Exam #1 Review

;;; Question #1

(defstruct triangle a b c)

(defun eq-tri (x)
   (and (listp x)
        (mapcar #'(lambda (s) 
                   (make-triangle :a s :b s :c s)
                  )
                x
        )
   )
)


;;; Question #2
(defun stars (y)
 (progn
  (format t "~%")
  (dotimes (yi y 'Done)
   (dotimes (x (+ yi 1) (format t "~%"))
    (format t "*")
   )
  )
 )
)

;; -- or --

(defun stars2 (y)
 (progn (format t "~%")
  (do ((i 0 (+ i 1)))
      ((= i y) 'Done)
      (do ((x 0 (+ x 1)))
          ((= x (+ i 1)) (format t "~%"))
          (format t "*")
      )
  )
 )
)

;;; Question #3
(defun array-adder (old-array len &optional (addit 0))
 (do ((new-arr (make-array len))
      (count 0 (+ count 1))
     )
     ((= count len) new-arr)
     (setf (aref new-arr count) (+ (aref old-array count) addit))
 )
)



;;; Question #4
(defun make-rectangle (&key (length 0) (width 0))
 (cons length width)
)

(defun rectangle-length (rect)
 (car rect)
)

(defun rectangle-width (rect)
 (cdr rect)
)

;;; Question #5a

(defstruct my-circle radius (area (* pi radius radius)) (circum (* 2 pi radius)))

;; #5b

(defun silly (rad1 rad2)
 (cond
  ((> rad1 rad2) (my-circle-area (make-my-circle :radius rad1)))
  ((> rad2 rad1) (my-circle-circum (make-my-circle :radius rad2)))
  (t 'EQUAL)
 )
)

;; #5c

(defun big-area (&rest radii)
 (my-circle-area (make-my-circle :radius (car (sort radii #'>))))
)

;; #5d

(defun cylinder (circ height)
 (and (my-circle-p circ)
      (let ((vol (* (my-circle-area circ) height))
            (sa (* (my-circle-circum circ) height))
           )
       (format t "~%The area is: ~A.  The volume is: ~A.  " sa vol)
       (if (> vol sa)
        ;then
         (format t "The volume is bigger.~%")
        ;else
        (format t "The surface area is bigger.~%")
       )
      )
 )
)

;; #5e

(let ((biggest-area nil))
 (defun biggest (circ)
  (cond
   ((not (my-circle-p circ)) biggest-area)
   ((null biggest-area) (setf biggest-area (my-circle-area circ)))
   ((> (my-circle-area circ) biggest-area) (setf biggest-area (my-circle-area circ)))
   (t biggest-area)
  )
 )
)