Why does merging these arrays cause an error?

My front-end and back-end code is listed below. It's working perfectly. And from this page I'm sending 2 arrays to another page. There I want to merge the arrays and insert into a MySQL table. Here it my front page.

<?php
    include("db.php");
    $team_id=$_GET['team_id'];
    $sql1=mysql_query("select members from team where team_开发者_StackOverflowid='$team_id'");
    $sql=mysql_query("select user_id,full_name from users where school_id= '1'");

    while($array=mysql_fetch_assoc($sql))
    {
        $x[] = $array['user_id'];
    }
    echo "</br>";
    $row1=mysql_fetch_array($sql1);
    $member=unserialize($row1['members']);
    echo "<form action='ad_team_mem_db.php' method='post'>";
    echo "<select name='mem[]' size='25' multiple='multiple'>";
    foreach(array_diff_assoc($x ,$member) as $item)
    {
        $sqlf=mysql_query("select user_id,full_name from users where school_id=1 and user_id='$item'");
        if($roww=mysql_fetch_array($sqlf)){
            echo "<option value='".$roww['user_id']."'>".$roww['full_name']."</option>";
        }
    }
    echo "</select></br>";
    echo "<input type='hidden' value='$member' name='member[]'>";
    echo "<input type='submit'>";
    echo "</form>";
    echo "</br>";
?>

And this is my backend page. In this page I couldn't merge 2 arrays.

<?
    include("db.php");
    $mem=$_POST['mem'];
    $member=$_POST['member'];
    **$members = array_merge ($member, $mem);**
?>

Error message,

Warning: array_merge() [function.array-merge]: Argument #1 is not an array in C:\AppServ\www\teen\ad_team_mem_db.php on line 5

At the point you do this:

echo "<input type='hidden' value='$member' name='member[]'>";

$member is a PHP array, and what you'll end up in the form will look like:

<input type='hidden' value='Array' name='member[]'>

which upon POSTing will be a simple string, which is why your array_merge is failing.

I think you probably need to unserialise the POST vars before merging.

try

$members = array_merge ((array) $member, (array) $mem);