Why variables do not persist between requests in PHP - Visual Breakdown

Concept Flow - Why variables do not persist between requests

Start Request 1

↓

Set variable $x = 5

↓

End Request 1 - Script stops

↓

Start Request 2

↓

Variable $x does NOT exist

↓

Set $x again or error

↓

End Request 2

Each web request runs a new PHP script instance, so variables set in one request are lost when it ends.

Execution Sample

PHP

<?php
$x = 5;
echo $x;
?>

This code sets $x to 5 and prints it during one request.

Execution Table

Step	Action	Variable $x	Output
1	Start Request 1	undefined
2	Set $x = 5	5
3	Print $x	5	5
4	End Request 1	5 (lost after script ends)
5	Start Request 2	undefined
6	Try to print $x	undefined	Error or empty
7	Set $x = 10	10
8	Print $x	10	10
9	End Request 2	10 (lost after script ends)

💡 Each request ends and clears all variables; no persistence between requests.

Variable Tracker

Variable	Start Request 1	After Step 2	After Step 4	Start Request 2	After Step 7	After Step 9
$x	undefined	5	lost	undefined	10	lost

Key Moments - 2 Insights

Why does $x lose its value after the first request ends?

Because PHP runs each request as a new script instance, all variables are cleared when the script finishes (see execution_table step 4).

Can variables keep their values automatically between requests?

No, variables do not persist automatically; you must use sessions, cookies, or databases to save data between requests.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of $x at the start of Request 2?

A undefined

B 5

C 10

D Error

💡 Hint

Check execution_table row 5 'Start Request 2' shows $x as undefined.

At which step does the variable $x get lost after being set?

A Step 6

B Step 3

C Step 4

D Step 7

💡 Hint

Look at execution_table step 4 where the request ends and variables are lost.

If you want $x to keep its value between requests, what should you do?

A Declare $x as global

B Use sessions or cookies

C Set $x again in each request

D Nothing, it persists automatically

💡 Hint

Refer to key_moments about persistence methods beyond normal variables.

Concept Snapshot

PHP variables exist only during one request.
When the script ends, all variables are cleared.
Each new request starts fresh with no previous variables.
To keep data between requests, use sessions, cookies, or databases.
Variables do NOT persist automatically across requests.

Full Transcript

In PHP, each web request runs the script from start to end. Variables like $x exist only during that request. When the request finishes, the script stops and all variables are lost. The next request starts fresh with no memory of previous variables. This is why $x set in one request is undefined in the next. To keep data between requests, you must use special storage like sessions or cookies. This example shows $x set to 5 in the first request and lost after it ends. In the second request, $x is undefined until set again. This behavior is normal and important to understand for web programming.

Practice

1. Why do PHP variables not keep their values between different page requests?

easy

A. Because PHP variables are saved only in cookies

B. Because PHP automatically deletes variables after 5 seconds

C. Because variables are stored only in the browser cache

D. Because each request starts a new script execution with fresh variables

Solution

1. Step 1: Understand PHP script execution

   Each time a PHP page loads, the server runs the script from the start with new variables.

2. Step 2: Recognize variable lifetime

   Variables exist only during that single script run and are lost after the page finishes loading.

3. Final Answer:

   Because each request starts a new script execution with fresh variables -> Option D

4. Quick Check:

   PHP variables reset each request = D [OK]

Hint: Remember: PHP runs fresh each page load, no memory kept [OK]

Common Mistakes:

• Thinking variables persist like JavaScript variables in browser
• Confusing PHP variables with cookies or sessions
• Assuming PHP stores variables on client side

2. Which of the following is the correct way to start a session in PHP to keep variables between requests?

easy

A. session_start();

B. start_session();

C. begin_session();

D. init_session();

Solution

1. Step 1: Recall PHP session function

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

2. Step 2: Verify syntax correctness

   Other options are not valid PHP functions and will cause errors.

3. Final Answer:

   session_start(); -> Option A

4. Quick Check:

   Use session_start() to begin sessions [OK]

Hint: Remember exact function name: session_start() [OK]

Common Mistakes:

• Using incorrect function names like start_session()
• Forgetting parentheses after function name
• Not calling session_start() before output

3. What will be the output of this PHP code on the second page load?

<?php
$counter = 0;
$counter++;
echo $counter;
?>

medium

A. 1

B. 2

C. 0

D. Error

Solution

1. Step 1: Analyze variable initialization

   Each page load sets $counter = 0;, so it resets every time.

2. Step 2: Increment and output

   Then $counter++ makes it 1, and echo prints 1.

3. Final Answer:

   1 -> Option A

4. Quick Check:

   Variable resets each load, so output is 1 [OK]

Hint: Variables reset each request unless stored externally [OK]

Common Mistakes:

• Assuming $counter keeps incrementing across requests
• Thinking output will be 2 or higher
• Expecting an error due to variable usage

4. This PHP code tries to keep a count between requests but always shows 1. What is the problem?

<?php
$counter = 0;
$counter++;
echo $counter;
?>

medium

A. The increment operator ++ is used incorrectly

B. The echo statement is missing a semicolon

C. Variables reset each request; no session or storage used

D. The variable $counter is not declared

Solution

1. Step 1: Identify variable reset issue

   The variable $counter is set to 0 on every request, so it never remembers previous value.

2. Step 2: Understand missing persistence method

   Without sessions or external storage, variables cannot keep values between requests.

3. Final Answer:

   Variables reset each request; no session or storage used -> Option C

4. Quick Check:

   Variables reset without session = B [OK]

Hint: Use sessions to keep variables between requests [OK]

Common Mistakes:

• Blaming increment operator for reset
• Thinking echo needs semicolon to work
• Assuming variable declaration is missing

5. You want to count how many times a user visits a page using PHP. Which approach correctly keeps the count between requests?

hard

A. Declare a global variable and increment it on each request

B. Use a session variable with session_start() and increment it

C. Use a local variable inside the script and increment it

D. Store the count in a variable inside the HTML code

Solution

1. Step 1: Understand variable lifetime

   Local and global PHP variables reset each request, so they can't keep count.

2. Step 2: Use sessions for persistence

   Sessions store data on the server between requests, so using session_start() and a session variable keeps count.

3. Final Answer:

   Use a session variable with session_start() and increment it -> Option B

4. Quick Check:

   Sessions keep data between requests = A [OK]

Hint: Use sessions to save data across page loads [OK]

Common Mistakes:

• Thinking global variables persist across requests
• Trying to store PHP variables in HTML
• Not starting session before using session variables