In what scenarios should constants be used instead of strings in PHP code?

Using constants instead of strings in PHP code is beneficial in scenarios where a value needs to be reused multiple times throughout the codebase. Constants provide a way to define a value once and then refer to it by its identifier throughout the code, making it easier to maintain and update the value in the future. This can help improve code readability, reduce errors caused by typos, and make it easier to track where a specific value is being used.

// Define a constant for a commonly used value
define('DB_HOST', 'localhost');
define('DB_USER', 'username');
define('DB_PASS', 'password');
define('DB_NAME', 'database');

// Example usage of constants
$connection = mysqli_connect(DB_HOST, DB_USER, DB_PASS, DB_NAME);
$query = "SELECT * FROM users";
$result = mysqli_query($connection, $query);