An Example Program

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 screen grab 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 ...

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