University of Washington CSE 154

Section 9: Cookies

Except where otherwise noted, the contents of this document are Copyright © Marty Stepp, Jessica Miller, and Victoria Kirst. All rights reserved. Any redistribution, reproduction, transmission, or storage of part or all of the contents in any form is prohibited without the author's expressed written permission.

Recall: Setting cookies in PHP

setcookie("name", "value");
...
$variable = $_COOKIE["name"];   # retrieve value of cookie later

setcookie("username", "martay");
setcookie("age", 19);
...
if (isset($_COOKIE["username"])) {
	$username = $_COOKIE["username"];
	print("Welcome back, $username.\n");
}

• any cookies sent by client are stored in $_COOKIE associative array
• use isset function to see whether a given cookie name exists

Exercise : Longcat Count (by Phil Sheperd)

Use a cookie (slides) to count the number of times the user has viewed longcat.php. Display this count to the user on the page, e.g. "You have visited 7 time(s)." (sample solution) For added challenge:

• Make the cat grow longer by repeating middle.jpg once for each page view.
• Make the page heading gain one more "o" in "Long" for each page view. (hint)
• Make the cookie expire after 10 seconds.

Exercise Solution

• longcat.php

Exercise : Prize (by Michael Beswetherick)

prize.php is a travel site. We want roughly every 10th visitor to win a "free trip". (sample solution)

• Every time the page loads, there should randomly be a 1-in-10 chance that the viewer wins a prize.
• If the user wins, show a congratulation message.
• Use a cookie to remember whether the current user has won the prize. If so, on all future page visits give them a link to redeem their prize.
• Give the user 24 hours to redeem the prize before the cookie expires. (Test it with very small values such as 10 seconds.)

Exercise Solution

• prize.php

Exercise : Birthdays (by Phil Sheperd)

What day of the month were you born on? Let's check the box for everyone's day in birthdays.php. The form submits to itself, but if you leave the page and come back, it forgets what boxes were checked.

• Remove the redundancy between all the checkboxes on the page using a loop.
• Use a cookie(s) to remember which checkboxes are checked when the form submits. If the user comes back, the same checkboxes should be checked.
  (How many cookies should you use, and what should you store in them?)
• (sample solution)

Exercise Solution

• birthdays.php
• birthdays.php (alternate version)