So let’s look at how a real life PHP program integrates with an HTML form by creating the program convert.php listed in Following Example. Type it in as shown and try it for yourself.
<?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; } ?>