How to get WordPress plugin url

When creating a wordpress theme, we often have to get the plugin url, so that we can load plugin css style file or javascript files.

For example, you have installed SyntaxHighlighter Evolved plugin, and you should load its wp-code-highlightjs/styles/default.css and wp-code-highlightjs/highlight.common.pack.js, then you must to know how to get wordpress plugin url.

We can use plugins_url() function get plugin url, for example:

<?php
$plugin_url = plugins_url();
echo $plugin_url;
?>

so we can use it in our theme.

<link rel="stylesheet" href="<?php echo plugins_url();?>/wp-code-highlightjs/styles/default.css">
<script src="<?php echo plugins_url();?>/wp-code-highlightjs/highlight.common.pack.js"></script>

,