passing form input name through hyperlink - php

Question

I am trying to pass input tag value to the another page to simply multiply the value of qty with price and return the updated price.The problem is when i pass the value of qty with get method it passes the value of qty only but does not pass another values.
cart.php
echo" <form method='get' name='form1' action='update_cart.php?id={$id}&name={$name}&price={$price}&qty=$_GET['qty']'>";//the problem comes here.
echo"<input type='number' name='qty' max='10'>
<input type='submit' value='update'></form>";
update_cart.php
$id = isset($_GET['id']) ? $_GET['id'] : "";
$name = isset($_GET['name']) ? $_GET['name'] : "";
$qty=isset($_GET['qty'])? $_GET['qty']: "";
$price=isset($_GET['price'])? $_GET['price']: "";
$price=$price*$qty;
header('Location: cart.php?action=quantity_updated&id=' . $id . '&name=' . $name . '&price='.$price . '&qty='.$qty);
when i click on update button after giving qty a value it shows something like this.
http://localhost/abc/cart.php?action=quantity_updated&id=&name=&price=0&qty=2

Answer 1

form method="get" passes variables automatically.
You do (and can) not need to append query string to the action attribute.
You do however need to represent those data in your form, if with <input type="hidden" name="qty" value="<?=$qty?>" /> style.

Answer 2

if you want pass some values , you can choose 2 way for it :
you can use the input with hidden type in you form.
if you use hidden type input you can use data just on one page.
<form method='get' action='?????'>
<input type='hidden' name='?????' value='?????'>
<input type='hidden' name='?????' value='?????'>
....
...
..
<input type='number' name='qty' max='10'/>
<input type='submit' value='submit'/>
</form>
you can use session for save data and use it in another page.
if you use session, you can use data in all php pages.
on page 1:
<?php
session_start();
$_SESSION['name']='value';
?>
on page 2:
<?php
session_start();
echo $_SESSION['name']; // value
?>

Answer 3

Your syntax for this line contains errors.
echo" <form method='get' name='form1' action='update_cart.php?id={$id}&name={$name}&price={$price}&qty=$_GET['qty']'>";
Change it to...
echo" <form method='get' name='form1' action='update_cart.php?id=".$id."&name=".$name."&price=".$price."&qty=".$_GET['qty']."'>";