$x = ["497", "498", "499", "500"];
$y = ["496", "497", "498", "499"];
$say = 0;
$yenidizi = array();
foreach($x as $a)
{
$yenidizi[$a] = $y[$say];
$say++;
}
print_r( $yenidizi );
?>Çıktı ;
Array ( [497] => 496 [498] => 497 [499] => 498 [500] => 499 )