Split foreach loop values

[mmarif4u]

Hi all,
I have a listbox, where user can select multiple entries, listbox is populated from database.

<select name="drop1[]" multiple="multiple">
<?php
$sql = mysql_query("select node_id,s_name,code from table order by node_id asc");
while($row = mysql_fetch_object($sql)){
echo "<option value='$row->node_id' selected='selected'>$row->node_id $row->s_name</option>";
}
?>
</select>

This part is working fine.
I am getting the values as:

$drop = $_POST['drop1'];
foreach($drop as $listbox){
echo $listbox;
} 

Now lets say, user selected three choices from listbox, and post holds ids like 1,2,3.
So what i want to do is split the values and use it outside foreach loop.
I tried exlpode function but in vain.

Any ideas.
Thanks.