<div style="font-family: 'Times New Roman'; font-size: 16px;">Sorry, <br _moz_dirty="" /><br _moz_dirty="" />But I don't understand what the modulo and my solution work together.<br _moz_dirty="" /><br _moz_dirty="" />Roelof<br _moz_dirty="" /><br /><br /><span>On 12/03/12, <b class="name">Matthias Felleisen </b> <matthias@ccs.neu.edu> wrote:</span><blockquote cite="mid:A9D3FD8E-D250-4C13-8FC5-BAC05D191C75@ccs.neu.edu" class="iwcQuote" style="border-left: 1px solid rgb(0, 0, 255); padding-left: 13px; margin-left: 0pt;" type="cite"><div class="mimepart text html"><span><p><table><tbody><tr><td style="word-wrap: break-word;"><p></p><div><br /></div><div>#lang racket</div><div><br /></div><div>(require 2htdp/image 2htdp/universe)</div><div><br /></div><div>; main : CarState -> CarState</div><div>; launch the program from some initial state</div><div>(define (main r)</div><div> (big-bang 0 (on-tick tock r) (to-draw render)))</div><div><br /></div><div>(define wheel-radius 5)</div><div>(define cab</div><div> (beside (rectangle (* 6 wheel-radius)(* 4 wheel-radius) "solid" "red") </div><div> (right-triangle (* 2 wheel-radius) (* 4 wheel-radius) "solid" "red")))</div><div>(define body</div><div> (rectangle (* 20 wheel-radius) (* 6 wheel-radius) "solid" "red"))</div><div>(define top</div><div> (above/align "right" cab body))</div><div>(define tire</div><div> (circle wheel-radius "solid" "black"))</div><div>(define bot</div><div> (beside tire</div><div> (rectangle (* 5 wheel-radius) (* 2 wheel-radius) "solid" "white")</div><div> tire))</div><div>(define auto</div><div> (above top bot))</div><div><br /></div><div>(define WIDTH 1000)</div><div>(define SPEED (* 0.54 (image-width auto)))</div><div>(define Y-CAR 50)</div><div>(define BACKGROUND (empty-scene WIDTH 200))</div><div><br /></div><div><br /></div><div>; CarState -> CarState</div><div>; the clock ticked; move the car by three pixels</div><div>; example:</div><div>; given: 20, expected 23</div><div>; given: 78, expected 81</div><div>(define (tock ws) </div><div> (modulo (+ ws SPEED) WIDTH)</div><div> #;</div><div> (if (< ws (-(image-width BACKGROUND) (* 0.54 (image-width auto))))</div><div> (+ ws 3)</div><div> ( - ws (image-width BACKGROUND))))</div><div><br /></div><div>; PositiveNumber -> Image</div><div>; run the animation at the specified rate [1/28 is decent, try 1/100 too]</div><div>(define (render ws)</div><div> (place-image auto ws Y-CAR BACKGROUND))</div><div><br /></div><div><br /></div><div><div>On Mar 12, 2012, at 10:24 AM, ROELOF WOBBEN wrote:</div><br class="Apple-interchange-newline" /><blockquote type="cite"><div style="font-family: 'Times New Roman'; font-size: 16px;">Hello, <br /><br />I have tried to make a function which display a car running on a empty-screen.<br />When the car is at the end. The car has to begin at the beginning.<br /><br />I have made this : <br /><br />(define wheel-radius 5)<br />(define cab (beside (rectangle (* 6 wheel-radius)(* 4 wheel-radius) "solid" "red")(right-triangle (* 2 wheel-radius) (* 4 wheel-radius) "solid" "red")))<br />(define body (rectangle (* 20 wheel-radius) (* 6 wheel-radius) "solid" "red"))<br />(define top (above/align "right" cab body))<br />(define tire (circle wheel-radius "solid" "black"))<br />(define bot (beside tire (rectangle (* 5 wheel-radius) (* 2 wheel-radius) "solid" "white") tire))<br />(define auto (above top bot))<br /><br />(define Y-CAR 50)<br />(define BACKGROUND (empty-scene 1000 200))<br /><br />; CarState -> CarState<br />; the clock ticked; move the car by three pixels<br />; example:<br />; given: 20, expected 23<br />; given: 78, expected 81<br />(define (tock ws) <br /> (if (< ws (-(image-width BACKGROUND)(* 0.54 (image-width auto))))(+ ws 3) ( - ws (image-width BACKGROUND))))<br /><br />; CarState -> Image<br />; place the car into a scene, according to the given world state<br />(define (render ws)<br /> (place-image auto ws Y-CAR BACKGROUND))<br /><br />; main : CarState -> CarState<br />; launch the program from some initial state<br />(define (main ws)<br /> (big-bang ws (on-tick tock) (to-draw render)))<br /><br />But now I wonder if I can do the same with setting the variable ws to zero.<br />So like this : If ws is smaller then the image-width increase with the half width of the car. then ws = ws+ 3 else ws = 0 <br /><br />Regards,<br /><br />Roelof<br /><br /><br /><br /><br /><br /> <br /><br /><br /><br /></div> ____________________<br /> Racket Users list:<br /> <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a><br /></blockquote></div><br /></td></tr></tbody></table></p></span></div></blockquote></div>