Listbox And Checkbox Validation

I am displaying some datas in listbox and checkbox which are gathered from the database. without choosing any of the checkbox and listbox if the user clicks the button i need to display an alert message. pls help. i am sending the code in which i am trying now.

LISTBOX
<select name="adminroles" >
<option value="" selected>--Select--</option>
<?
$admin_roles = mysql_query ("select * from role_master");
$admin_roles= mysql_num_rows($admin_roles);
for($k=0;$k<$admin_roles;$k++)
{
?>
<option value= "<? echo mysql_result($admin_roles,$k,role_id); ?>">
<? echo mysql_result($admin_roles,$k,role_name);?> </option>
<?
}
?>
</select>

<input type="checkbox" value="<? echo mysql_result($res1,$z,function_id);?>" name="chk[]" <? if($edit_func_id == mysql_result($res1,$z,function_id)){?>
checked<? } ?> >