<?php
if (empty($_POST['name'])) // Determine whether a variable is empty
{
$errors[] = 'Please enter a name';
}

if (empty($_POST['age']))
{
$errors[] = 'Please enter a age';
}
else if (!is_numeric($_POST['age']))
{
$errors[] = 'Please enter a valid age with a numeric value';
}

if (empty($_POST['email']))
{
$errors[] = 'Please enter an e-mail';
}
else if (!eregi("^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9-]+(\.[a-z0-9-]+)*(\.[a-z]{2,3})$", $_POST['email']))
{
$errors[] = 'Please enter a valid e-mail address';
// eregi ? Case insensitive regular expression match
}

if (empty($_POST['comments']))
{
$errors[] = 'Please enter some comments';
}
else if (strlen ($_POST['comments']) > 255)
{
$errors[] = 'Your comment is too long, please do not submit more then 255 characters';
}
// count ? Count elements in an array, or properties in an object
if (count($errors) == 0)
{
// Process form
}
else
{
echo $errors[0];
}
?>

<form method="post">
<table>
<tr>
<td>Name:</td>
<td><input type="text" name="name"></td>
</tr>
<tr>
<td>Age:</td>
<td><input type="text" name="age"></td>
</tr>
<tr>
<td>E-mail:</td>
<td><input type="text" name="email"></td>
</tr>
<tr>
<td>Comments:</td>
<td><input name="comments" ></td>
</tr>
<tr>
<td colspan="2"><input type="submit" name="submit"></td>
</tr>
</table>
</form>