Php升级抛出数组和foreach（）的错误

so I just started using a new php and none of my functions are working in the same proper way. I have a shopping cart function that checks for items in a session array and then it places the item in the array. If the item already it exitis it updates that input by the qty entered.

$arr=$_SESSION['item'];


function searchForId($id, $array) {
    if (is_array($array)) {

   foreach ($array as $key => $val) {
       if ($val['sku'] === $id) {
           return $key;
       }
    }
   return 'no';
    }
}


$theSearch = searchForId($sku, $arr);


if(!isset($_SESSION['item']))
 {
  $newitem = array ('sku' => $sku , 'qty' => $qty);

  $_SESSION['item'][1] = $newitem;
 }
 else
 {


 if ($theSearch != 'no') {

   $nqty= $_SESSION['item'][$theSearch]['qty'] + $qty;
   $_SESSION['item'][$theSearch]['qty'] = $nqty;

 }
else
{
if(count($_SESSION['item']) >=1)
{
     $newitem = array ('sku' => $sku , 'qty' => $qty);
     $_SESSION['item'][] = $newitem;    
}
 else
{
     $newitem = array ('sku' => $sku , 'qty' => $qty);
     $_SESSION['item'][1] = $newitem;   
}
}



}

The error im getting is that the line $nqty= $_SESSION['item'][$theSearch]['qty'] + $qty; and the error thrown is

Fatal error: Cannot use string offset as an array in

Can someone please help!