Data Validation

[Paulo Monteiro]

I have the next PHP code:


PHP Code:
<select name="day" id="day" tabindex="3">
<?php
for($n=1; $n <=31; $n++)
{
?>
<option value="<? echo $n ?>"><? echo $n ?></option>
<?
}
?>

</select>

<select name="month" id="month" tabindex="3">
<?php
for($n=1; $n <=12; $n++)
{
?>
<option value="<? echo $n ?>"><? echo $n ?></option>
<?
}
?>
</select>


<select name="year" id="year" tabindex="3">

<?php for($i=0;$i<3;$i++) { ?>
<option><?php echo(date('Y') - $i); ?></option>
<?php } ?>

</select>

I wan´t to validate the data input. How can I do it??