Setting and reading cookies in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code that sets and reads a cookie?

Consider the following PHP code snippet that sets a cookie and then tries to read it immediately. What will be the output?

PHP

<?php
setcookie('user', 'Alice', time() + 3600);
if (isset($_COOKIE['user'])) {
    echo $_COOKIE['user'];
} else {
    echo 'No cookie found';
}
?>

A Alice

B Empty string

C Undefined index error

D No cookie found

💡 Hint

Remember that cookies set by setcookie() are not available until the next page load.

The setcookie() function sends a cookie header to the browser, but the $_COOKIE superglobal is not updated until the next request. So immediately after setting, $_COOKIE['user'] is not set, resulting in 'No cookie found'.

🧠 Conceptual

intermediate

Which PHP function is used to set a cookie?

In PHP, which function is used to send a cookie to the browser?

A cookie_set()

B sendcookie()

C setcookie()

D createcookie()

💡 Hint

The function name starts with 'set'.

The correct function to set a cookie in PHP is setcookie(). Other options are invalid function names.

❓ Predict Output

advanced

What will be the output of this PHP code reading a cookie?

Given the following PHP code, what will be the output if the cookie 'session' is set to 'xyz123'?

PHP

<?php
if (!empty($_COOKIE['session'])) {
    echo 'Session ID: ' . $_COOKIE['session'];
} else {
    echo 'No session cookie';
}
?>

A Session ID: xyz123

B No session cookie

C Undefined index: session

D Session ID:

💡 Hint

Check if the cookie exists and is not empty.

If the cookie 'session' is set to 'xyz123', the condition !empty($_COOKIE['session']) is true, so it prints 'Session ID: xyz123'.

🔧 Debug

advanced

Why does this PHP code fail to delete a cookie?

Examine the code below. It tries to delete a cookie named 'theme' but fails. What is the reason?

PHP

<?php
setcookie('theme', '', time() + 3600);
if (!isset($_COOKIE['theme'])) {
    echo 'Cookie deleted';
} else {
    echo 'Cookie still exists';
}
?>

A setcookie() cannot delete cookies

B The expiration time should be in the past to delete a cookie

C Cookie name is incorrect

D Cookie value cannot be empty

💡 Hint

To delete a cookie, you must expire it immediately.

To delete a cookie, you must set its expiration time to a past time. Setting it to time() + 3600 sets it to expire in the future, so it remains.

🚀 Application

expert

How many cookies will be sent to the browser after this PHP script runs?

Consider this PHP script that sets multiple cookies. How many cookies will the browser receive?

PHP

<?php
setcookie('a', '1', time() + 3600);
setcookie('b', '2', time() + 3600, '/path1');
setcookie('c', '3', time() + 3600, '/path2');
setcookie('a', '4', time() + 3600, '/path1');
?>

A 4

B 1

C 2

D 3

💡 Hint

Cookies with the same name but different paths are treated as separate cookies.

The script issues four setcookie() calls, each producing a distinct Set-Cookie header. The two 'a' cookies differ by path (default '/' vs '/path1'), making all four unique: 'a' (path '/'), 'b' (path '/path1'), 'c' (path '/path2'), 'a' (path '/path1'). Thus, 4 cookies are sent.

Practice

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

easy

A. To store small pieces of data on the user's computer

B. To execute server-side scripts

C. To connect to a database

D. To style the webpage

Solution

1. Step 1: Understand what cookies do

   Cookies save small data on the user's computer to remember information like preferences or login status.

2. Step 2: Identify the correct purpose

   Among the options, only storing small data on the user's computer matches the purpose of cookies.

3. Final Answer:

   To store small pieces of data on the user's computer -> Option A

4. Quick Check:

   Cookies = store small data [OK]

Hint: Cookies save small data on user devices [OK]

Common Mistakes:

• Confusing cookies with server-side code execution
• Thinking cookies connect to databases
• Assuming cookies control webpage style

2. Which of the following is the correct way to set a cookie named user with value John in PHP?

easy

A. setcookie('user', 'John');

B. cookie_set('user', 'John');

C. set_cookie('user', 'John');

D. setcookie(user, John);

Solution

1. Step 1: Recall the correct function name and syntax

   The PHP function to set cookies is setcookie(), which takes the cookie name and value as strings.

2. Step 2: Check the options for correct syntax

   Only setcookie('user', 'John'); uses the correct function name and quotes around name and value.

3. Final Answer:

   setcookie('user', 'John'); -> Option A

4. Quick Check:

   Use setcookie() with quoted strings [OK]

Hint: Use setcookie() with quotes around name and value [OK]

Common Mistakes:

• Using wrong function names like cookie_set or set_cookie
• Not quoting the cookie name and value
• Confusing cookie setting with reading

3. What will be the output of the following PHP code if the cookie color is set to blue?

<?php
if (isset($_COOKIE['color'])) {
    echo $_COOKIE['color'];
} else {
    echo 'No color set';
}
?>

medium

A. color

B. No color set

C. Error: Undefined index

D. blue

Solution

1. Step 1: Check if the cookie 'color' exists

   The code uses isset() to check if $_COOKIE['color'] is set. Since the cookie is set to 'blue', this condition is true.

2. Step 2: Output the cookie value

   Because the cookie exists, the code echoes its value, which is 'blue'.

3. Final Answer:

   blue -> Option D

4. Quick Check:

   Cookie exists, so output its value [OK]

Hint: Check isset before reading cookie to avoid errors [OK]

Common Mistakes:

• Assuming cookie is not set and printing default
• Not using isset and causing undefined index error
• Confusing cookie name with its value

4. Identify the error in this PHP code that tries to read a cookie named session:

<?php
echo $_COOKIE['session'];
?>

medium

A. Cookie name should be uppercase

B. Wrong function used to read cookie

C. Missing check if cookie exists before reading

D. Cookies cannot be read in PHP

Solution

1. Step 1: Understand cookie reading best practice

   Directly accessing $_COOKIE['session'] without checking if it exists can cause an undefined index notice if the cookie is not set.

2. Step 2: Identify the missing check

   The code should use isset($_COOKIE['session']) before echoing to avoid errors.

3. Final Answer:

   Missing check if cookie exists before reading -> Option C

4. Quick Check:

   Always check isset() before reading cookie [OK]

Hint: Always check isset() before using $_COOKIE values [OK]

Common Mistakes:

• Ignoring isset() check causing warnings
• Thinking cookie names are case sensitive in $_COOKIE
• Believing cookies cannot be read in PHP

5. You want to set a cookie named theme with value dark that expires in 7 days. Which code correctly sets this cookie?

hard

A. setcookie('theme', 'dark', time() + 60);

B. setcookie('theme', 'dark', time() + 7 * 24 * 60 * 60);

C. setcookie('theme', 'dark', 7);

D. setcookie('theme', 'dark', time() - 7 * 24 * 60 * 60);

Solution

1. Step 1: Calculate expiration time for 7 days

   7 days in seconds = 7 * 24 hours * 60 minutes * 60 seconds = 604800 seconds.

2. Step 2: Use time() plus 7 days for expiration

   The expiration parameter in setcookie() should be current time plus 604800 seconds.

3. Step 3: Check options for correct expiration

   setcookie('theme', 'dark', time() + 7 * 24 * 60 * 60); correctly uses time() + 7 * 24 * 60 * 60. setcookie('theme', 'dark', time() + 60); sets only 60 seconds, C uses 7 (invalid), D sets a past time (cookie expires immediately).

4. Final Answer:

   setcookie('theme', 'dark', time() + 7 * 24 * 60 * 60); -> Option B

5. Quick Check:

   Expire = now + 7 days in seconds [OK]

Hint: Expire time = time() + days * 86400 seconds [OK]

Common Mistakes:

• Using small numbers like 7 or 60 instead of seconds
• Setting expiration in the past
• Forgetting to add time() to expiration