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PHP 101 (part 3): Looping The Loop
Learn how to repeatedly execute code with loops and more sophisticated conditional tests.

| Creative Conditionals |

Normally, when creating and processing forms in PHP, you would place the HTML form in one file, and handle form processing through a separate PHP script. However, with the power of conditional statements at your disposal, you can combine both pages into one.

How do you do this? Simple. All you need to do is assign a name to the form submit control, and then check whether the special $_POST container variable contains that name when the script first loads up. If it does, the form has already been submitted, and you can process the data; if it does not, that the user has not submitted the form and you therefore need to generate the initial, unfilled form. Thus, by testing for the presence or absence of this submit variable, a clever PHP programmer can use a single PHP script to generate both the initial form, and the output after it has been submitted, as appropriate.

Here's a simple example:


<html>
<head></head>
<body>

<?php
/* if the "submit" variable does not exist, the form has not been submitted - display initial page */
if (!isset($_POST['submit'])) {
?>

    <form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
    Enter your age: <input name="age" size="2">
    <input type="submit" name="submit" value="Go">
    </form>

<?php
    }
else {
/* if the "submit" variable exists, the form has been submitted - look for and process form data */
    // display result
    $age = $_POST['age'];
    if ($age >= 21) {
        echo 'Come on in, we have alcohol and music awaiting you!';
        }
    else {
        echo 'You\'re too young for this club, come back when you\'re a little older';
    }
}
?>

</body>
</html>


As you can see, the script contains two pages: the initial, empty form and the result page generated after hitting the submit button. In order to decide which page to display, the script first tests for the presence of the $_POST['submit'] variable. If it doesn't find it, it assumes that the form has yet to be submitted, and displays the initial list of days. Once the form has been submitted, the same script will be called to process the form input. This time, however, the $_POST['submit'] variable will be set, and so PHP will not display the initial page, but rather the page containing the result message.

Note that for this to work, your submit button must have a value assigned to its "name" attribute, and you must check for that value in the primary conditional statement. And in case you were wondering, the $_SERVER array is a special PHP variable which always holds server information, including the path and name of the currently executing script.

Next up, loops.


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