Session variables in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a session variable in PHP?

A session variable is a way to store information (like user data) on the server for a user to use across multiple pages during their visit.

beginner

How do you start a session in PHP?

You start a session by calling session_start(); at the very beginning of your PHP script before any output.

beginner

How do you set a session variable in PHP?

After starting the session, you set a session variable like this: $_SESSION['key'] = 'value';

beginner

How do you access a session variable in PHP?

After starting the session, you access a session variable by using $_SESSION['key'] to get its value.

intermediate

Why do you need to call session_start() on every page that uses session variables?

Because session_start() tells PHP to resume the existing session or start a new one, so session variables are available on that page.

What function do you use to begin a session in PHP?

A session_start()

B start_session()

C begin_session()

D init_session()

The correct function to start a session in PHP is session_start().

Where are session variables stored?

A On the server

B In the user's browser cookies

C In the HTML code

D In a database automatically

Session variables are stored on the server, not in the user's browser or HTML.

How do you set a session variable named 'user' to 'Alice'?

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

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

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

D session->user = 'Alice';

You set a session variable using the superglobal array $_SESSION like this: $_SESSION['user'] = 'Alice';

What must you do before accessing any session variables on a page?

A Call session_access()

B Call session_start()

C Include a session.php file

D Nothing special is needed

You must call session_start() before accessing session variables to ensure the session is active.

Which superglobal array holds session variables in PHP?

A $_COOKIE

B $_GET

C $_POST

D $_SESSION

Session variables are stored in the $_SESSION superglobal array.

Explain how to create, store, and access a session variable in PHP.

Think about what you do at the start of the page and how you use the $_SESSION array.

Why is it important to call session_start() on every page that uses session variables?

Consider what happens if you try to use $_SESSION without starting the session.

Practice

1. What is the main purpose of using session_start() in PHP?

easy

A. To connect to a database

B. To send output to the browser

C. To begin a session and enable session variables

D. To include another PHP file

Solution

1. Step 1: Understand what session_start() does

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

2. Step 2: Identify the purpose of session variables

   Session variables store user data across multiple pages, but they only work if a session is started first.

3. Final Answer:

   To begin a session and enable session variables -> Option C

4. Quick Check:

   session_start() = start session [OK]

Hint: Remember: session_start() must be called before using $_SESSION [OK]

Common Mistakes:

• Thinking session_start() connects to a database
• Using session variables without calling session_start()
• Confusing session_start() with output functions

2. Which of the following is the correct way to set a session variable named user with the value "Alice"?

easy

A. $_SESSION['user'] = 'Alice';

B. session['user'] = 'Alice';

C. set_session('user', 'Alice');

D. session_start['user'] = 'Alice';

Solution

1. Step 1: Recall the syntax for setting session variables

   Session variables are stored in the global $_SESSION array, so you assign values like $_SESSION['key'] = value;.

2. Step 2: Check each option's syntax

   $_SESSION['user'] = 'Alice'; uses the correct $_SESSION superglobal with proper array syntax and assignment.

3. Final Answer:

   $_SESSION['user'] = 'Alice'; -> Option A

4. Quick Check:

   $_SESSION['key'] = value [OK]

Hint: Use $_SESSION['name'] = value to set session data [OK]

Common Mistakes:

• Using session without the $_SESSION superglobal
• Trying to call session_start as an array
• Using undefined functions like set_session()

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

session_start();
$_SESSION['count'] = 1;
$_SESSION['count']++;
echo $_SESSION['count'];

medium

A. 1

B. 0

C. Error

D. 2

Solution

1. Step 1: Analyze session variable initialization and increment

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

2. Step 2: Determine the final value of $_SESSION['count']

   After increment, the value becomes 2, which is then printed by echo.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   1 incremented by 1 = 2 [OK]

Hint: Increment session variable with ++ after setting it [OK]

Common Mistakes:

• Forgetting to call session_start() before using $_SESSION
• Assuming $_SESSION['count'] stays 1 after ++
• Expecting an error due to session usage

4. Identify the error in this PHP code snippet:

$_SESSION['user'] = 'Bob';
echo $_SESSION['user'];

medium

A. Missing session_start() before using $_SESSION

B. Incorrect array syntax for $_SESSION

C. Cannot assign string to $_SESSION

D. Echo statement syntax is wrong

Solution

1. Step 1: Check for session initialization

   The code uses $_SESSION but does not call session_start() first, which is required to access session variables.

2. Step 2: Verify syntax correctness

   The array syntax and echo statement are correct, and assigning a string to $_SESSION is valid.

3. Final Answer:

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

4. Quick Check:

   Always call session_start() before $_SESSION [OK]

Hint: Always start session with session_start() before $_SESSION use [OK]

Common Mistakes:

• Using $_SESSION without session_start()
• Thinking $_SESSION needs special syntax
• Assuming 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 using session variables?

hard

A. session_start();
$_SESSION['visits']++;
echo $_SESSION['visits'];

B. session_start();
if (!isset($_SESSION['visits'])) {
$_SESSION['visits'] = 1;
} else {
$_SESSION['visits']++;
}
echo $_SESSION['visits'];

C. session_start();
$_SESSION['visits'] = 1;
echo $_SESSION['visits'];

D. if (!isset($_SESSION['visits'])) {
$_SESSION['visits'] = 1;
} else {
$_SESSION['visits']++;
}
echo $_SESSION['visits'];

Solution

1. Step 1: Ensure session is started

   Calling session_start() is necessary to use session variables.

2. Step 2: Check visit count logic

   The code checks if $_SESSION['visits'] exists; if not, it sets it to 1. Otherwise, it increments the count. This correctly tracks visits.

3. Step 3: Verify output

   Finally, it echoes the current visit count, showing how many times the user visited during the session.

4. Final Answer:

   Code snippet with session_start() and visit count check -> Option B

5. Quick Check:

   Initialize then increment visits with session_start() [OK]

Hint: Always check isset() before incrementing session counters [OK]

Common Mistakes:

• Forgetting session_start() before using $_SESSION
• Not checking if session variable exists before increment
• Resetting visit count every page load