Flag bad words by a bad words list

flag_bad_words.php

<?php
function flagWords($text, $badwords)
{
    $badword = reset($badwords);
    while ($badword) {
        $text = preg_replace(
            '/('. preg_quote($badword) .')/i',
            '<span style="color:red;">$1</span>',
            $text
        );
        $badword = next($badwords);
    }

    $text = preg_replace(
        '/\d+/i',
        '<span style="color:red;">$0</span>',
        $text
    );

    return $text;
}