Notice: Undefined variable a

<?

if($_GET["page"]==4)
{
	$a == $_SESSION["id"];
}
elseif($_GET["page"]==3)
{
//regel 8
	$a == $_GET["id"];
}

$i=0;
//15
	foreach($objLoadGebruiker->loadGebruiker($a) as $value)
	{ 
		$sortarray[] = 	$value;
                  //de rest van de code
             }$i++;
?>

<?
 
if($_GET["page"]==4)
{
	$a == $_SESSION["id"];
}
elseif($_GET["page"]==3)
{
//regel 8
	$a == $_GET["id"];
}
 
$i=0;
//15
	foreach($objLoadGebruiker->loadGebruiker($a) as $value)
	{ 
		$sortarray[] = 	$value;
                  //de rest van de code
             }$i++;
?>

$a = $_SESSION["id"];

$a = $_SESSION["id"];