Php wordpress help

I am writing the following code for making a plugin

<?php
header("Content-Type: text/css");
/*
Plugin Name: Name of the plugin.
Plugin URI: The page having information related to plugin.
Version: 0.1
Description: Your plugin description.
Author: Your name
Author URI: Author's website.
*/
?>
<?php
function box()
{
?><div class="box">
<p><b>Author:</b> <?php the_author_link(); ?><p>
<?php echo get_avatar( get_the_author_email(), '50' ); ?>
<p><?php the_author_description(); ?></p>
</div>
<?php
}
function style() {
echo "
<style>
<!--
.avatar{
float:left;
background-color: #fff;
border:1px solid #ccc;
padding: 4px;
margin: 0 7px 2px 0;
display: inline;
}
.box{
color: #666;
font-weight: normal;
background: #fff;
border: 1px solid #ccc;
padding: 12px;
margin-bottom:8px;
}
-->
</style>
";
}
function author_box_ContentFilter($content)
{
if (is_single())
return $content.box().style();
else
return $content;
}

add_filter('the_content', 'author_box_ContentFilter');
?>

PHP:

This code is appending the author info box at the start of post.But i want to add the box a the end of post.I also tried

{
if (is_single())
return box().$content.style();
else
return $content;
}

PHP:

But this is also not working.
Seeking for help to append the box at the end of post.
Thanks in anticipation

 

The problem is that you are outputting the box directly instead of appending it to the $content
change it so that the box function returns the box content as a string

 

Thanks for your reply.Will you please give me the exact code.What should i write instead of that?I will be thankful to you.

 

<?php

/*
Plugin Name: Name of the plugin.
Plugin URI: The page having information related to plugin.
Version: 0.1
Description: Your plugin description.
Author: Your name
Author URI: Author's website.
*/

function box() {
	$content = '<div class="box">
<p><b>Author:</b> '.the_author_link().'<p>
'.get_avatar(get_the_author_email(), '50').'
<p>'.the_author_description().'</p>
</div>';
	return $content;
}
function style() {
	return "
<style>
<!--
.avatar{
float:left;
background-color: #fff;
border:1px solid #ccc;
padding: 4px;
margin: 0 7px 2px 0;
display: inline;
}
.box{
color: #666;
font-weight: normal;
background: #fff;
border: 1px solid #ccc;
padding: 12px;
margin-bottom:8px;
}
-->
</style>
";
}
function author_box_ContentFilter($content) {
	if (is_single()) return $content.box().style();
	else  return $content;
}

add_filter('the_content', 'author_box_ContentFilter');

?>

PHP:

Something like that should work

 

But jay the problem is,only gravatar is showing.Other template tags are not working e.g the_author_description and the_author_link