Form Validation

Hi. Welcome to Bytes!

PHP has many useful functions that help with validation.
htmlspecialchars and htmlentities will strip away HTML tags from the output, making safe to output again.

If you plan on using this in a SQL query, you can use addslashes to make sure quotes and back-slashes will make it through without errors. (Assuming you don't have magic_quotes enabled)
There are also some database specific features you can use, like mysql_real_escape_string for MySQL databases.

For a more specific validation, like say to validate email addresses, you would be best of using regular expressions, using PHPs preg_match or ereg functions.

As to your second problem.
<?=__post('Username');?> is not valid PHP.
The shorthand syntax (<? ?> or <?= ?>) is no longer enabled by default in PHP. You would have to enable it in your php.ini configuration file to use it.

It's always better to use the normal syntax (<?php ?>).
Or in your case: <?php echo $_POST['Username']; ?>

Thanks for your help. Really appreciate.