How to Pass a PHP Interview: Top Questions and Answers

Introduction

An interview for a PHP developer position is not only a test of language syntax but also a test of understanding architecture, security, and modern approaches. Many candidates get lost on basic questions because they don't prepare systematically. In this article, we will break down the top questions most often asked in PHP interviews, with code examples and explanations. The material will be useful for both beginners and experienced developers looking to refresh their knowledge.

Data Types and Type Casting

What data types exist in PHP?

PHP supports 8 basic data types, divided into three groups:

• Scalar: bool, int, float, string.
• Compound: array, object, callable, iterable.
• Special: resource, null.

Example of type checking:

$value = "123";if (is_numeric($value)) {    $intValue = (int) $value; // casting to int    var_dump($intValue); // int(123)}

What is the difference between == and ===?

The == operator compares values after type casting, while === compares without casting (strict comparison). This is one of the most common pitfalls:

var_dump(0 == "0");   // bool(true)var_dump(0 === "0");  // bool(false)

OOP in PHP: Inheritance, Interfaces, and Traits

What are traits and why are they needed?

Traits are a code reuse mechanism in PHP that solves the problem of single inheritance. A trait cannot be instantiated, but it can be included in a class using use:

trait Logger {    public function log($message) {        echo "[LOG]: $message";    }}

class User {    use Logger;}

$user = new User();$user->log("User created");

What is the difference between an abstract class and an interface?

• Abstract class can contain method implementations and properties. It is inherited via extends.
• Interface defines only method signatures (without implementation). A class can implement multiple interfaces via implements.

interface CanFly {    public function fly();}

abstract class Bird {    abstract public function sound();    public function eat() {        echo "Eats grain";    }}

class Eagle extends Bird implements CanFly {    public function sound() { echo "Scream"; }    public function fly() { echo "Flies"; }}

Working with Databases and PDO

What is PDO and why is it used?

PDO (PHP Data Objects) is an extension for working with databases that provides a unified interface for different DBMS (MySQL, PostgreSQL, SQLite, etc.). The main advantage is protection against SQL injections through prepared statements:

$pdo = new PDO('mysql:host=localhost;dbname=test', 'user', 'pass');$stmt = $pdo->prepare('SELECT * FROM users WHERE email = :email');$stmt->execute([':email' => 'user@example.com']);$user = $stmt->fetch(PDO::FETCH_ASSOC);

How to handle errors in PDO?

The best practice is to switch PDO to exception mode:

$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);try {    $pdo->exec("INSERT INTO users (name) VALUES ('John')");} catch (PDOException $e) {    echo "Error: " . $e->getMessage();}

Security and Common Vulnerabilities

How to protect an application from XSS and SQL injections?

In an interview, it is important to show understanding not only of theory but also of practical measures:

• SQL injections: use PDO with prepared statements (see example above).