redirecting to a URL query string - php

Question

I am trying to redirect a page to:
product_page.php?rest_id=$rest_id&area=$rest_city
for example:
product_page.php?rest_id=3&area=Enfield
At the moment the page is redirecting to:
http://localhost/PhpProject2/product_page.php?rest_id=&area=
Even though i have specified :
if (isset($_GET['rest_id'])){
$rest_id = mysqli_real_escape_string($dbc,$_GET['rest_id']);
}
if (isset($_GET['area'])){
$area = mysqli_real_escape_string($dbc,$_GET['area']);
}
if (isset($_GET['add_item'])) {
(int)$_GET['add_item']]){
$_SESSION['Shopping_cart_' . (int) $_GET['add_item']]+='1';
//redirect
echo"<script>window.open('product_page.php?rest_id=$rest_id&area=$rest_city','_self')</script>"; //header does not work
}
How would i go about getting the echo to re-direct to the correct page.
What i have tried:
Calling both add_item, rest_id and rest_city in the same if asset.
Moving the $_GET rest_id and rest_city closing tag after the echo.
The two above options just stop the page from re-directing all together, this is my first time doing this, any suggestions or tips would be greatly appreciated.

Answer 1

You should use double qotes ["string $variable string"] for variable to work inside a string or if not you should concatenate the string with [.] sign.
echo"<script>window.open('product_page.php?rest_id=$rest_id&area=$rest_city','_self')</script>";
This will not work because of single qoute [']
Regards

Answer 2

There are many syntax errors in your code. Also, the way you echo the string is wrong. You need to concat the variables with the string, using the PHP concatenation operator, else use double quotes.
Below fixed your errors:
if (isset($_GET['rest_id'])){
$rest_id = mysqli_real_escape_string($dbc,$_GET['rest_id']);
}
if (isset($_GET['area'])){
$area = mysqli_real_escape_string($dbc,$_GET['area']);
}
if (isset($_GET['add_item'])) {
$_SESSION['Shopping_cart_'] = (int) $_GET['add_item']+='1';
echo"<script>window.open('product_page.php?rest_id=" . $rest_id . "&area=" . $rest_city . "','_self')</script>";
}