Accessing class instances in an array - php

Question

I'm working on a project, and I've come across an issue that has me stumped. The code below is a class file and a test page to make sure it's working. It's for somebody else who is programming the site, otherwise I would code the JSON output differently. Basically, the person implementing it just has to pull a bunch of data (like below) from a database, and loop through, instantiating a class object for each result, and plugging each instance into an array, and passing the array to the printJson function, which will print the JSON string. Here is what I have:
Results.php
<?php
class Result
{
public $Category = NULL;
public $Title = NULL;
public $Price = NULL;
public function __construct($category, $title, $price)
{
$this->Category = $category;
$this->Title = $title;
$this->Price = $price;
}
public static function printJson($arrayOfResults)
{
$output = '{"results": [';
foreach ($arrayOfResults as $result)
{
$output += '{"category": "' . $result->Category . '",';
$output += '"title": "' . $result->Title . '",';
$output += '"price": "' . $result->Price . '",';
$output += '},';
}
$output = substr($output, 0, -1);
$output += ']}';
return $output;
}
}
?>
getResults.php
<?php
require_once('Result.php');
$res1 = new Result('food', 'Chicken Fingers', 5.95);
$res2 = new Result('food', 'Hamburger', 5.95);
$res3 = new Result('drink', 'Coke', 1);
$res4 = new Result('drink', 'Coffee', 2);
$res5 = new Result('food', 'Cheeseburger', 6.95);
$x = $_GET['x'];
if ($x == 1)
{
$array = array($res1);
echo Result::printJson($array);
}
if ($x == 2)
{
$array = array($res1, $res2);
echo Result::printJson($array);
}
if ($x == 3)
{
$array = array($res1, $res2, $res3);
echo Result::printJson($array);
}
if ($x == 5)
{
$array = array($res1, $res2, $res3, $res4, $res5);
echo Result::printJson($array);
}
?>
The end result is if I go to getResults.php?x=5, it will return $res1 thru $res5 (again, this is just to test, I would never do something like this in production) formatted as JSON. Right now, I get '0' outputted and I cannot for the life of me figure out why. Could my foreach loop not be written properly? Please, any help you could provide would be awesome!

Answer 1

It's because you're using + for concatenation rather than .:
$output .= '{"category": "' . $result->Category . '",';
$output .= '"title": "' . $result->Title . '",';
$output .= '"price": "' . $result->Price . '",';
$output .= '},';
But you should really not construct the JSON yourself, as it leads to a number of errors making for invalid JSON (trailing commas etc). Use something like this instead:
public static function printJson(array $arrayOfResults)
{
$results['results'] = array_map('get_object_vars', $arrayOfResults);
return json_encode($results);
}