Top Mistakes of Beginner PHP Developers: How to Avoid Them

Introduction

PHP remains one of the most popular languages for web development, despite the emergence of many alternatives. However, beginners often make typical mistakes that can lead to vulnerabilities, reduced performance, or simply non-working code. In this article, we will analyze the top 5 mistakes of novice PHP developers, show examples of incorrect code, and give recommendations for fixing them. The material will be useful both for those who are just starting to learn PHP and for those who want to refresh their knowledge.

1. Ignoring Security: SQL Injections and XSS

The most common and dangerous mistake is insufficient filtering of user data. Many beginners take data directly from $_GET or $_POST and insert it into SQL queries or output it to the page without escaping.

Incorrect Code (SQL Injection)

<?php$username = $_POST['username'];$password = $_POST['password'];

// Vulnerable query$sql = "SELECT * FROM users WHERE username = '$username' AND password = '$password'";$result = mysqli_query($conn, $sql);?>

If an attacker enters the value ' OR '1'='1 in the username field, the query will return all users, and login will be performed without a password.

Correct Code (Using Prepared Statements)

<?php$stmt = $conn->prepare("SELECT * FROM users WHERE username = ? AND password = ?");$stmt->bind_param("ss", $username, $password);$stmt->execute();$result = $stmt->get_result();?>

The same applies to outputting data in HTML. Always use htmlspecialchars() to escape special characters:

<?phpecho htmlspecialchars($user_input, ENT_QUOTES, 'UTF-8');?>

2. Neglecting Strict Typing

PHP is a dynamically typed language, and beginners often rely on automatic type coercion. This can lead to unexpected results, especially in comparisons.

Example of Non-Obvious Behavior

<?php$value = "100 apples";if ($value == 100) {    echo "Equals 100"; // Will output "Equals 100"!}?>

The string "100 apples" is implicitly converted to the number 100, so the condition is true. Use strict comparison (===) and strict typing in modern projects:

Recommendations

• Declare declare(strict_types=1); at the beginning of each file.
• Use strict comparison === and !== instead of == and !=.
• Explicitly specify types for function arguments and return values.

<?phpdeclare(strict_types=1);

function calculateTotal(float $price, int $quantity): float {    return $price * $quantity;}?>

3. Memory Leaks and Inefficient Resource Management

Beginners often forget to close files, database connections, or free memory after working with large data. PHP's garbage collector works automatically, but this does not mean you can ignore resource management.

Typical Mistake: Unclosed Connection

<?php$conn = new mysqli($host, $user, $pass, $db);// ... a lot of code ...// Forgot to call $conn->close();?>

Correct Approach: Using try-finally or Resource Managers

<?php$conn = new mysqli($host, $user, $pass, $db);try {    // work with DB} finally {    $conn->close();}?>

For working with files, use fopen()/fclose() in pairs, and for large arrays, use unset() after use. In modern versions of PHP, you can use generators (yield) to process large data sets without loading everything into memory.

4. Mixing Logic and Presentation