Undefined index: cart in C:\xampp\htdocs\yes\cart.php

Question

**Undefined index: cart in C:\xampp\htdocs\yes\cart.php **

dont know how to get rid of it.

   <?php

it shows error here.

    $cart = unserialize(serialize($_SESSION['cart']));

     for($i=0; $i<count($cart); $i++)
     {
      ?>


      <tr>
       <td> <?php echo $cart[$i]->id;  ?> </td>
        <td> <?php echo $cart[$i]->product_name;  ?> </td>
         <td> <?php echo $cart[$i]->price;  ?> </td>
          <td> <?php echo $cart[$i]->details;  ?> </td>
        <td> <?php echo $cart[$i]->category;  ?> </td>
         <td> <?php echo $cart[$i]->subcategory;  ?> </td>
          <td> <?php echo $cart[$i]->price*$cart[$i]->quantity;  ?> </td>
       </tr>

     <?php } ?>

      </table>

      <br />

i am stucked here. please take me out from here