JSON encoding and decoding in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using json_encode?

Consider the following PHP code snippet. What will it output?

PHP

<?php
$array = ['name' => 'Alice', 'age' => 30, 'active' => true];
echo json_encode($array);
?>

A {"name":"Alice","age":30,"active":true}

B {"name":"Alice","age":"30","active":"true"}

C {"name":Alice,"age":30,"active":true}

D Array

💡 Hint

Remember json_encode converts PHP arrays to JSON strings with proper quotes and types.

json_encode converts the PHP associative array into a JSON string with keys and values properly quoted and boolean true as true without quotes.

❓ Predict Output

intermediate

What does json_decode return with second parameter true?

What will be the output of this PHP code?

PHP

<?php
$json = '{"fruit":"apple","count":5}';
$result = json_decode($json, true);
var_dump($result);
?>

A array(2) { ["fruit"]=> string(5) "apple" ["count"]=> int(5) }

B object(stdClass)#1 (2) { ["fruit"]=> string(5) "apple" ["count"]=> int(5) }

C string(23) "{"fruit":"apple","count":5}"

D NULL

💡 Hint

The second parameter true makes json_decode return an associative array.

json_decode with true returns an associative array, so var_dump shows array with keys and values.

❓ Predict Output

advanced

What error does this PHP code raise when decoding invalid JSON?

What error or output will this PHP code produce?

PHP

<?php
$invalidJson = '{"name":"Bob", age: 25}';
$result = json_decode($invalidJson);
if (json_last_error() !== JSON_ERROR_NONE) {
    echo json_last_error_msg();
} else {
    var_dump($result);
}
?>

A NULL

B Control character error, possibly malformed UTF-8 characters

C Syntax error, malformed JSON

D Syntax error

💡 Hint

Look at the JSON string: keys must be quoted strings.

The JSON string is invalid because the key 'age' is not quoted, causing a syntax error in JSON parsing.

🧠 Conceptual

advanced

Which option correctly encodes a PHP object to JSON with private properties?

Given a PHP class with private properties, which code snippet will correctly encode its public data to JSON?

PHP

<?php
class User {
    private string $name;
    private int $age;
    public function __construct(string $name, int $age) {
        $this->name = $name;
        $this->age = $age;
    }
    public function toArray(): array {
        return ['name' => $this->name, 'age' => $this->age];
    }
}
$user = new User('Eve', 28);
// Which line below correctly encodes the user data?

A echo json_encode($user);

B echo json_encode($user->toArray());

C echo json_encode(get_object_vars($user));

D echo json_encode((array)$user);

💡 Hint

Private properties are not accessible directly; use a method to expose data.

json_encode only encodes public properties by default. Using toArray() exposes data as an array for encoding.

🚀 Application

expert

How many items are in the array after decoding this JSON string?

Given this PHP code, how many items does the resulting array contain?

PHP

<?php
$json = '[{"id":1,"tags":["php","json"]},{"id":2,"tags":[]},{"id":3}]';
$array = json_decode($json, true);
echo count($array);
?>

A 1

B 2

C 3

D 0

💡 Hint

Count the top-level elements in the JSON array.

The JSON string is an array with 3 objects, so count($array) returns 3.