Session variables in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP session code?

Consider the following PHP code that uses session variables. What will be printed?

PHP

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

A 2

B 1

C 3

D Undefined index error

💡 Hint

Remember that session variables keep their values during the session and you can update them like normal variables.

The session variable 'count' is first set to 1, then incremented by 1, so the output is 2.

❓ Predict Output

intermediate

What error does this PHP session code produce?

What error will this PHP code produce when run?

PHP

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

A Warning: session_start() not called

B No error, outputs 'Alice'

C Fatal error: Undefined variable 'SESSION'

D Parse error: syntax error

💡 Hint

Session variables require a special function to be called before using them.

Without session_start(), PHP produces a warning that the session has not been started. Accessing $_SESSION without starting the session is not recommended and may cause warnings or unexpected behavior.

🔧 Debug

advanced

Why does this PHP session code not keep the value?

This PHP code tries to count page visits using a session variable but always prints 1. Why?

PHP

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

A The variable 'visits' is not initialized before use

B The else block resets 'visits' to 1 every time, so it never increments

C PHP sessions are disabled on the server

D session_start() is missing, so session variables don't work

💡 Hint

Look carefully at what happens inside the else block.

The else block sets 'visits' back to 1 every time, so the count never increases beyond 1.

❓ Predict Output

advanced

What is the output of this PHP session code with unset?

What will this PHP code output?

PHP

<?php
session_start();
$_SESSION['name'] = 'Bob';
unset($_SESSION['name']);
echo isset($_SESSION['name']) ? $_SESSION['name'] : 'No name';
?>

A Empty string

B Bob

C Undefined index error

D No name

💡 Hint

What does unset() do to a session variable?

unset() removes the session variable, so isset() returns false and 'No name' is printed.

❓ Predict Output

expert

What is the output of this PHP session code with session_destroy?

What will this PHP code output?

PHP

<?php
session_start();
$_SESSION['color'] = 'red';
session_destroy();
echo isset($_SESSION['color']) ? $_SESSION['color'] : 'No color';
?>

A Warning: session has been destroyed

B No color

C red

D Empty string

💡 Hint

Does session_destroy() immediately clear the $_SESSION array in the current script?

session_destroy() ends the session but does not clear the $_SESSION superglobal in the current script, so 'red' is printed.

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