How can PHP be used to track and display the number of users currently online on a website?

To track and display the number of users currently online on a website, we can use PHP sessions to keep track of active users. We can increment a counter when a user visits the site and decrement it when they leave. By storing this information in a session variable, we can display the count of active users on the website.

// Start or resume a session
session_start();

// Increment the online users count
if (!isset($_SESSION['online_users'])) {
    $_SESSION['online_users'] = 1;
} else {
    $_SESSION['online_users']++;
}

// Display the number of online users
echo "Online Users: " . $_SESSION['online_users'];