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Using Hidden Fields to Save State

The script in Listing 10.6 has no way of knowing how many guesses a user has made, but we can use a hidden field to keep track of this. A hidden field behaves exactly the same as a text field, except that the user cannot see it unless he views the HTML source of the document that contains it.

Take the original numguess.php script, and save a copy as numguess2.php. In the new version, add a line after the initial assinment of the $num_to_guess variable:

$num_tries = (isset($_POST[num_tries])) ? $num_tries + 1 : 1;

This line initializes a variable called $num_TRies, and assigns a value to it. If the form has not yet been submitted ($_POST[num_tries] is empty), the value of the $num_TRies variable is 1 because we will be on our first attempt at guessing the number. If the form has already been sent, then the new value is the value of $_POST[num_tries], plus 1.

The next change comes after the HTML level H1 heading:

<p><strong>Guess number:</strong> <?php echo $num_tries; ?></p>

This new line simply prints the current value of $num_tries to the screen.

Finally, before the HTML code for the form submission button, add the hidden field. This field will save the incremented value of $num_TRies:

<input type="hidden" name="num_tries" value="<?php echo $num_tries; ?>">

Listing 10.7 shows the new script, in its entirety.

Listing 10.7. Saving State with a Hidden Field
1: <?php
2: $num_to_guess = 42;
3: $num_tries = (isset($_POST[num_tries])) ? $_POST[num_tries] + 1 : 1;
4: if (!isset($_POST[guess])) {
5:    $message = "Welcome to the guessing machine!";
6: } else if ($_POST[guess] > $num_to_guess) {
7:    $message = "$_POST[guess] is too big! Try a smaller number.";
8: } else if ($_POST[guess] < $num_to_guess) {
9:    $message = "$_POST[guess] is too small! Try a larger number.";
10: } else { // must be equivalent
11:    $message = "Well done!";
12: }
13: $guess = $_POST[guess];
14: ?>
15: <html>
16: <head>
17: <title> Saving state with a hidden field</title>
18: </head>
19: <body>
20: <h1><?php echo $message ?></h1>
21: <p><strong>Guess number:</strong> <?php echo $num_tries; ?></p>
22: <form action="<?php echo $_SERVER[PHP_SELF]; ?>" method="POST">
23: <p><strong>Type your guess here:</strong>
24: <input type="text" name="guess" value="<?php echo $guess; ?>">
25: <input type="hidden" name="num_tries" value="<?php echo $num_tries; ?>">
26: <p><input type="submit" value="submit your guess"></p>
27: </form>
28: </body>
29: </html>

Save the numguess2.php file, and place it in your Web server document root. Access the form a few times with your Web browser, and try to guess the number (pretend you don't already know it). The counter should increment by one, with each access.

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