Can't increment product's quantity in session object

PHP
1

I created an object, it’s named carwash. I created a session and assigned that object for session, if I enter quantity then and press buy button, I have result (example 6):

Your shopping cart contains 6 items.

but when I enter nothing, I get:

Your shopping cart contains items.

How should I do? Thank you! Here is all my code:

index.php


<?php
	session_start();
	
	require_once 'carwash.php';
	if (isset($_SESSION['encoded_cartopass'])) {
		// first let's get the variable from the session
		$encoded_cartopass = $_SESSION['encoded_cartopass'];
		
		// now let's unpack it
		$cartopass = unserialize($encoded_cartopass);
		
		// echo quantity
		echo "Your shopping cart contains {$cartopass->getQuantity()} items. <br /><br />";
	}
	else {
		echo "Your shopping cart contains 0 items. <br /><br />";
	}
?>

<form action="process.php" method="post">
	Quantity: <input type="text" name="quantity" id="quantity"/>
	<input type="submit" value="Buy" name="submit" />
</form>

process.php


<?php

	require_once 'carwash.php';

	if (isset($_POST['submit'])) {
		
		if (!isset($_SESSION['encoded_cartopass'])) {
			
			// construct and set quantity
			$cartopass = new carwash();
			$cartopass->setQuantity($_POST['quantity']);
			
			// construct and encode session
			session_register('encoded_cartopass');
			$_SESSION['encoded_cartopass'] = serialize($cartopass);
		}
		else {
			// if session is existing, decode it and
			// increment quantity
			$encoded_cartopass = $_SESSION['encoded_cartopass'];
			
			$cartopass = unserialize($encoded_cartopass);
			
			$cartopass->incrementQuantity($_POST['quantity']);
			
			// encode class and assign to session and
			// session is used pass to index.php
			$_SESSION['encode_cartopass'] = serialize($cartopass);
		}
		
	}
	
	echo "<script>window.location.href='index.php'</script>";
?>

carwash.php


<?php
	class carwash {
		
		private $carmake;
		private $caryear;
		private $quantity;
		
		public function getCarmake() {
			return $this->carmake;
		}
		
		public function setCarmake($carmake) {
			$this->carmake = $carmake;
		}
		
		public function getCaryear() {
			return $this->caryear;
		}
		
		public function setCaryear($caryear) {
			$this->caryear = $caryear;
		}
		
		public function getQuantity() {
			return $this->quantity;
		}
		
		public function setQuantity($quantity) {
			$this->quantity = $quantity;
		}
		
		public function incrementQuantity($quantity = '') {
			if (empty($quantity)) {
				$this->quantity++;
			}
			else {
				$this->quantity += $quantity;
			}
		}
		
		public function washcar() {
			echo "scruba, dub, dub, scruba, dub, dub <br />";
			echo "I'm feelling cleaner, Thank you!";
		}
	}
?>
2

The if statement is the problem:

<?php
    if (isset($_SESSION['encoded_cartopass'])) {
        // echo quantity
        echo "Your shopping cart contains {$cartopass->getQuantity()} items. <br /><br />";
    }
    else {
        echo "Your shopping cart contains 0 items. <br /><br />";
    }
?>

$_SESSION[‘encoded_cartopass’]) is set but it contains an empty (not set) $cartopass->getQuantity()

3

I found in Java document (and ASP.NET) that session can store an object but I just knew, in PHP, it’s limited. So, I use encode and decode aproach to passing object to another page. I did, thank you.