Notice: Undefined variable: id in C:\xampp\htdocs\feedback\index.php on line 21 php code example

Example: undefined index: tec_comm in c:\xampp\htdocs\fossee\user5.php on line 45

<?php require_once('../Connections/itemconn.php'); ?>
    <?php   

    $id=$_GET['id']; 

        $query=mysql_query("select * from manuf where id='$id' ")or die(mysql_error());
        $row=mysql_fetch_array($query);

        ?>

<form action="updateprice.php" method="post" enctype="multipart/form-data">
  <table align="center">
   <tr>
   <td> <label><strong>Item Name</strong></label></td>
     <td> <label> <?php echo $row['itemname']; ?></label><input type="hidden" name="id" value="<?php echo $id; ?> " />
     <br /></td>
    </tr>
    <tr>

     <td><label><strong>Unit price </strong></label></td>
  <td> <input type="text" name="pass" value="<?php echo $row['unitprice']; ?> " /><br /></td>
  </tr>

    <tr>
  <td> 
          <input type="reset" name="Reset" value="CANCEL" />
      <br></td>


     <td> 
          <input type="submit" name="Submit2" value="Update" />      </td>
   </tr>
</table>
</form>
</body>
</html>