Convert BBcode to HTML and Vice-Versa

bbcode-html.php

<?php
//This function let convert BBcode to HTML
function bbcode_to_html($text)
{
    $text = nl2br(htmlentities($text, ENT_QUOTES, 'UTF-8'));
    $in = array(
        '#\[b\](.*)\[/b\]#Usi',
        '#\[i\](.*)\[/i\]#Usi',
        '#\[u\](.*)\[/u\]#Usi',
        '#\[s\](.*)\[/s\]#Usi',
        '#\[img\](.*)\[/img\]#Usi',
        '#\[url\]((ht|f)tps?\:\/\/(.*))\[/url\]#Usi',
        '#\[url=((ht|f)tps?\:\/\/(.*))\](.*)\[/url\]#Usi',
        '#\[left\](.*)\[/left\]#Usi',
        '#\[center\](.*)\[/center\]#Usi',
        '#\[right\](.*)\[/right\]#Usi'
    );
    $out = array(
        '<strong>$1</strong>',
        '<em>$1</em>',
        '<span style="text-decoration:underline;">$1</span>',
        '<span style="text-decoration:line-through;">$1</span>',
        '<img src="$1" alt="Image" />',
        '<a href="$1">$1</a>',
        '<a href="$1">$4</a>',
        '<div style="text-align:left;">$1</div>',
        '<div style="text-align:center;">$1</div>',
        '<div style="text-align:right;">$1</div>'
    );
    $count = count($in) - 1;
    for ($i = 0; $i <= $count; $i++) {
        $text = preg_replace($in[$i], $out[$i], $text);
    }
    return $text;
}

//This function let convert HTML to BBcode
function html_to_bbcode($text)
{
    $text = str_replace('<br />', '', $text);
    $in = array(
        '#<strong>(.*)</strong>#Usi',
        '#<em>(.*)</em>#Usi',
        '#<span style="text-decoration:underline;">(.*)</span>#Usi',
        '#<span style="text-decoration:line-through;">(.*)</span>#Usi',
        '#<img src="(.*)" alt="Image" />#Usi',
        '#<a href="(.*)">(.*)</a>#Usi',
        '#<div style="text-align:left;">(.*)</div>#Usi',
        '#<div style="text-align:center;">(.*)</div>#Usi',
        '#<div style="text-align:right;">(.*)</div>#Usi'
    );
    $out = array(
        '[b]$1[/b]',
        '[i]$1[/i]',
        '[u]$1[/u]',
        '[s]$1[/s]',
        '[img]$1[/img]',
        '[url=$1]$2[/url]',
        '[left]$1[/left]',
        '[center]$1[/center]',
        '[right]$1[/right]'
    );
    $count = count($in) - 1;
    for ($i = 0; $i <= $count; $i++) {
        $text = preg_replace($in[$i], $out[$i], $text);
    }
    return $text;
}