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.

Practice

1. What is the main purpose of using sessions in PHP?

easy

A. To remember user data across multiple pages

B. To store data permanently on the user's computer

C. To speed up the website loading time

D. To create a new database connection

Solution

1. Step 1: Understand what sessions do

   Sessions keep track of user information as they move between pages on a website.

2. Step 2: Compare options

   Only To remember user data across multiple pages correctly describes this purpose. Options A, C, and D describe unrelated functions.

3. Final Answer:

   To remember user data across multiple pages -> Option A

4. Quick Check:

   Sessions remember user data = B [OK]

Hint: Sessions remember data across pages, not store on user PC [OK]

Common Mistakes:

• Confusing sessions with cookies stored on user device
• Thinking sessions speed up page loading
• Believing sessions create database connections

2. Which PHP function must be called before using $_SESSION variables?

easy

A. session_end()

B. session_open()

C. session_init()

D. session_start()

Solution

1. Step 1: Identify the correct function to start a session

   The function session_start() initializes a session or resumes the current one.

2. Step 2: Check other options

   Functions like session_end(), session_open(), and session_init() do not exist in PHP.

3. Final Answer:

   session_start() -> Option D

4. Quick Check:

   Start session with session_start() = C [OK]

Hint: Always call session_start() before accessing $_SESSION [OK]

Common Mistakes:

• Using non-existent functions like session_end()
• Forgetting to call session_start() before $_SESSION
• Calling session_start() after outputting HTML

3. What will be the output of this PHP code?

<?php
session_start();
$_SESSION['count'] = 1;
$_SESSION['count']++;
echo $_SESSION['count'];
?>

medium

A. 2

B. Error

C. 0

D. 1

Solution

1. Step 1: Analyze session variable assignment and increment

   The code sets $_SESSION['count'] to 1, then increments it by 1, making it 2.

2. Step 2: Output the session variable

   The echo statement prints the current value, which is 2.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   1 incremented by 1 = 2 [OK]

Hint: Increment after setting 1 results in 2 [OK]

Common Mistakes:

• Assuming the value stays 1 without increment
• Thinking session variables reset each time
• Expecting an error without session_start()

4. Identify the error in this PHP code snippet:

<?php
$_SESSION['user'] = 'Alice';
echo $_SESSION['user'];
?>

medium

A. Cannot assign string to $_SESSION

B. Incorrect variable name, should be $SESSION

C. Missing session_start() before using $_SESSION

D. Echo statement syntax is wrong

Solution

1. Step 1: Check session initialization

   The code uses $_SESSION without calling session_start() first, which is required.

2. Step 2: Verify other options

   Variable name $_SESSION is correct, strings can be assigned, and echo syntax is valid.

3. Final Answer:

   Missing session_start() before using $_SESSION -> Option C

4. Quick Check:

   session_start() needed before $_SESSION = A [OK]

Hint: Always call session_start() before $_SESSION usage [OK]

Common Mistakes:

• Forgetting session_start() causes undefined $_SESSION
• Confusing $_SESSION with $SESSION
• Thinking echo syntax is incorrect

5. You want to count how many times a user visits a page during a session. Which code snippet correctly implements this?

hard

A. <?php
$_SESSION['visits'] = 1;
echo $_SESSION['visits'];
?>

B. <?php
session_start();
if (!isset($_SESSION['visits'])) {
$_SESSION['visits'] = 1;
} else {
$_SESSION['visits']++;
}
echo "Visits: " . $_SESSION['visits'];
?>

C. <?php
session_start();
$_SESSION['visits']++;
echo $_SESSION['visits'];
?>

D. <?php
session_start();
$_SESSION['visits'] = 0;
echo $_SESSION['visits'];
?>

Solution

1. Step 1: Check session initialization and visit count logic

   <?php session_start(); if (!isset($_SESSION['visits'])) { $_SESSION['visits'] = 1; } else { $_SESSION['visits']++; } echo "Visits: " . $_SESSION['visits']; ?> starts the session, checks if 'visits' exists, initializes or increments it properly.

2. Step 2: Review other options for errors

   <?php $_SESSION['visits'] = 1; echo $_SESSION['visits']; ?> lacks session_start(), <?php session_start(); $_SESSION['visits']++; echo $_SESSION['visits']; ?> increments without initialization, <?php session_start(); $_SESSION['visits'] = 0; echo $_SESSION['visits']; ?> resets visits to 0 every time.

3. Final Answer:

   The code snippet that initializes visits=1 if not set, else increments -> Option B

4. Quick Check:

   Initialize then increment visits with session_start() = A [OK]

Hint: Initialize visits if not set, then increment [OK]

Common Mistakes:

• Not calling session_start() before $_SESSION
• Incrementing without checking if variable exists
• Resetting counter on every page load