An Example Program

So let’s look at how a real life PHP program integrates with an HTML form by creating the program convert.php listed in Example 11-10. Type it in as shown and try it for yourself.

Example 11-10. A program to convert values between Fahrenheit and Celsius
<?php // convert.php
$f = $c = "";

if (isset($_POST['f'])) $f = sanitizeString($_POST['f']);
if (isset($_POST['c'])) $c = sanitizeString($_POST['c']);

if ($f != '')
{
    $c = intval((5 / 9) * ($f - 32));
    $out = "$f °f equals $c °c";
}
elseif($c != '')
{
    $f = intval((9 / 5) * $c + 32);
    $out = "$c °c equals $f °f";
}
else $out = "";

echo <<<_END
<html><head><title>Temperature Converter</title>
</head><body><pre>
Enter either Fahrenheit or Celsius and click on Convert

<b>$out</b>
<form method="post" action="convert.php">
Fahrenheit <input type="text" name="f" size="7" />
   Celsius <input type="text" name="c" size="7" />
           <input type="submit" value="Convert" />
</form></pre></body></html>
_END;

function sanitizeString($var)
{
    $var = stripslashes($var);
    $var = htmlentities($var);
    $var = strip_tags($var);
    return $var;
}
?>

When you call up convert.php in a browser, the result should look something like the screenshot in Figure 11-8.

The temperature conversion program in action
Figure 11-8. The temperature conversion program in action

To break the program down, the first line initializes the variables $c and $f in case they do not get posted to the program. The next two lines ...

Get Learning PHP, MySQL, and JavaScript now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.

Start your free trial