多选下拉菜单 - 如何添加默认值

I'm trying to add default value in multiselect dropdown, so far i tried

    <select name="addons[]" multiple="multiple" id="addons">
     <option value="Not Selected" <?php echo set_select('addons[]', 'Not Selected', TRUE); ?> >Not Selected</option>
    <?php foreach ($addons as $options) { ?>
    <option value="<?php echo $options->addon_name; ?>"><h5><?php echo $options->addon_name; ?></h5></option>
    <?php } ?>                 
 </select>

I should suppose to get the default value as "Not selected" but i'm getting only empty. Any one knows where i'm going wrong ?

<select name="addons[]" multiple="multiple" id="addons">
 <option value="Not Selected" 
<?php echo in_array("Not Selected",$addons)?"SELECTED":"" ?> 
>Not Selected</option>
<?php foreach ($addons as $options) { ?>
    <option value="<?php echo $options->addon_name; ?>" 
    <?php echo in_array($options->addon_name,$addons)?"SELECTED":"" ?>
    ><h5><?php echo $options->addon_name; ?></h5></option>
<?php } ?>                 
</select>

where $addons is for example the $_POST['addons'] or the array of current addons from your database.

By the way: I think you should not use < h5 > inside the < option > tag