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Open Source Technologies

Notes has been submitted; otherwise, we’d attempt to assess variables that aren’t yet made available.
We can test for submission by testing for the existence of the variable $_POST[guess], which is
made available if your script has been sent a “guess” parameter. If $_POST[guess] isn’t present,
we can safely assume that the user arrived at the page without submitting a form. If the value
is present, we can test the value it contains. The test for the presence of the $_POST[guess]
variable takes place on line 4.

Listing 7 A PHP Number-Guessing Script
1. < ?php

2. $num_to_guess = 42;
3. $message = “”;
4. if (!isset($_POST[guess])) {
5. $message = “Welcome to the guessing machine!”;

6. } elseif ($_POST[guess] > $num_to_guess) {
7. $message = “$_POST[guess] is too big! Try a smaller number”;
8. } elseif ($_POST[guess] < $num_to_guess) {
9. $message = “$_POST[guess] is too small! Try a larger number”;

10. } else { // must be equivalent
11. ?>

9.5 Using Hidden Fields to Save State

The script in Listing 7 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. Listing 8 adds a hidden field to the number-guessing script and some PHP to work with it.
Listing 8 Saving State with a Hidden Field

1. < ?php
2. $num_to_guess = 42;

3. $num_tries = (isset($_POST[num_tries])) ? $num_tries + 1 : 0;
4. $message = “”;
5. if (!isset($_POST[guess])) {

6. $message = “Welcome to the guessing machine!”;
7. } elseif ($_POST[guess] > $num_to_guess) {

8. $message = “$_POST[guess] is too big! Try a smaller number”;
9. } elseif ($_POST[guess] < $num_to_guess) {
10. $message = “$_POST[guess] is too small! Try a larger number”;

11. } else { // must be equivalent
12. $message = “Well done!”;

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