php outputting script

I am trying to output from mysql database, the code i have, which is just before the opening html tag, is this below

<?php include('connecting_file.php');
$catid=$_GET['cat'];
$subid=$_GET['subcat'];
if (!function_exists("GetSQLValueString")) {
function GetSQLValueString($theValue, $theType, $theDefinedValue = "", $theNotDefinedValue = "") 
{
  $theValue = get_magic_quotes_gpc() ? stripslashes($theValue) : $theValue;

  $theValue = function_exists("mysql_real_escape_string") ? mysql_real_escape_string($theValue) : mysql_escape_string($theValue);

  switch ($theType) {
    case "text":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;    
    case "long":
    case "int":
      $theValue = ($theValue != "") ? intval($theValue) : "NULL";
      break;
    case "double":
      $theValue = ($theValue != "") ? "'" . doubleval($theValue) . "'" : "NULL";
      break;
    case "date":
      $theValue = ($theValue != "") ? "'" . $theValue . "'" : "NULL";
      break;
    case "defined":
      $theValue = ($theValue != "") ? $theDefinedValue : $theNotDefinedValue;
      break;
  }
  return $theValue;
}
}

mysql_select_db($database_name, $pmo);
$query_cat = "select * from subcat where catid='$catid'and subid='$subid'";
$cat = mysql_query($query_cat, $pmo) or die(mysql_error());
$row_cat = mysql_fetch_assoc($cat);
$totalRows_cat = mysql_num_rows($cat);
?>

Then i use this one to output the content from the table by just adding this code to where i want content to appear

<?php echo $row_cat['content']; ?>

but all i get is

Notice: Undefined index: cat in C:\wamp\www\mysite\aboutus.php on line 2

Notice: Undefined index: subcat in C:\wamp\www\mysite\aboutus.php on line 3

Can someone please help me out

Both $_GET['cat'] and $_GET['subcat'] have no value. Their values need to be sent in the URL string, and checked for before attempting to use them, or executing any code that relies on their values being present.