How sessions work in PHP - Practice Exercises

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP session code?

Consider this PHP script that uses sessions. What will it output?

PHP

<?php
session_start();
if (!isset($_SESSION['count'])) {
    $_SESSION['count'] = 1;
} else {
    $_SESSION['count']++;
}
echo $_SESSION['count'];
?>

A 1

B 0

C An error about undefined index

D A blank page

💡 Hint

Think about what happens the first time the session variable is set.

The code starts a session and checks if 'count' exists in the session. If not, it sets it to 1. Then it prints the value. On the first run, it prints 1.

🧠 Conceptual

intermediate

What does session_start() do in PHP?

Choose the correct explanation of what session_start() does in PHP.

A It initializes a session or resumes the current one based on a session identifier passed via a cookie or URL.

B It destroys all session data and ends the session immediately.

C It creates a new session file on the server without checking for existing sessions.

D It encrypts all session variables automatically.

💡 Hint

Think about how PHP knows which session belongs to which user.

session_start() either creates a new session or resumes an existing one by checking the session ID sent by the client, usually via a cookie.

🔧 Debug

advanced

Why does this PHP session code cause a warning?

Look at this PHP code snippet. It causes a warning about headers already sent. Why?

PHP

<?php
session_start();
echo "Hello";
session_start();
?>

A Because <code>echo</code> cannot be used with sessions.

B Because <code>session_start()</code> is called twice, and output was sent before the second call.

C Because sessions must be started after all output is sent.

D Because <code>session_start()</code> requires a parameter.

💡 Hint

Headers must be sent before any output. What happens if you call session_start() after output?

Calling session_start() sends HTTP headers. If output is sent before, headers cannot be sent again, causing a warning.

📝 Syntax

advanced

Which option correctly sets a session variable in PHP?

Choose the correct way to set a session variable named user with value admin.

A set_session('user', 'admin');

B session['user'] = 'admin';

C $_SESSION['user'] = 'admin';

D session->user = 'admin';

💡 Hint

Remember the superglobal array used for sessions.

Session variables are stored in the $_SESSION superglobal array. The other options are invalid syntax or functions.

🚀 Application

expert

How many items are stored in the session after this code runs?

Given this PHP code, how many session variables exist after execution?

PHP

<?php
session_start();
$_SESSION['a'] = 1;
$_SESSION['b'] = 2;
unset($_SESSION['a']);
$_SESSION['c'] = 3;
?>

A 3

B 0

C 1

D 2

💡 Hint

Think about what unset() does to session variables.

The code sets three session variables but removes 'a' with unset(). So only 'b' and 'c' remain, totaling 2.