ตรวจสอบ code ให้หน่อยครับ ผมรับค่าจากฟรอม แบบมีเงื่อนไขในการประกาศตัวแปร

<form name="form1" method="post" action="input_detail.php">
  <p>
    <select name="combo" id="combo">
      <option value="combobox1">combobox1</option>
      <option value="combobox2">combobox2</option>
    </select>
  </p>
  <p>
    <input type="checkbox" name="checkbox[]" value="checkbox1">
    <label for="checkbox">checkbox</label>
  </p>
  <p>
    <label for="combobox"></label>
    <input type="checkbox" name="checkbox[]" value="checkbox2" />
  checkbox2  </p>
  <p>
    <input type="submit" name="button" id="button" value="Submit">
  </p>
</form>

<?

include"config.php" ;


$checkbox = $_POST['checkbox'];
$combobx = $_POST['combo'];

if( $_REQUEST['combo']=='combobox1'  && $_REQUEST['checkbox[]']=='checkbox1' )
{
$price='200';
}
if( $_REQUEST['combo']=='combobox1'  && $_REQUEST['checkbox[]']=='checkbox2' )
{
$price='300';
}


$val = "";
if (isset($checkbox))
    $val = implode($checkbox, ",");
	
$price = "";
if (isset($price))
    $price = $price++;	


$sql = "insert into testxxx(comboxxx,chekxxx,totalxxx) value ('$combobx','$val','$price')";
$objQuery = mysql_query($sql);

			echo '<script type="text/javascript">'; 
			echo 'alert("input in price");'; 
			echo 'window.location.href = "x3.php";';
			echo '</script>';
		
		
	mysql_close();

?>