Variable scope in functions in PHP - Step-by-Step Execution

Concept Flow - Variable scope in functions

Start Program

↓

Define Global Variable

↓

Call Function

↓

Inside Function

↓

Access Global?

↓

Use global var

↓

Function Ends

↓

Back to Global

↓

Program Ends

This flow shows how a program defines a global variable, calls a function, and how variables inside the function can be local or access the global variable.

Execution Sample

PHP

<?php
$number = 10;
function test() {
  $number = 5;
  echo $number;
}
test();
echo $number;
?>

This code shows a global variable and a local variable with the same name inside a function, printing both.

Execution Table

Step	Code Line	Variable	Value	Action	Output
1	$number = 10;	number	10	Global variable set
2	function test() {...}	-	-	Function defined
3	test();	-	-	Function called
4	$number = 5;	number (local)	5	Local variable inside function set
5	echo $number;	number (local)	5	Print local variable	5
6	Function ends	-	-	Return to global scope
7	echo $number;	number (global)	10	Print global variable	10

💡 Function ends and program finishes after printing both local and global variables.

Variable Tracker

Variable	Start	After Function Call	Final
number (global)	10	10	10
number (local)	undefined	5	undefined

Key Moments - 3 Insights

Why does echo inside the function print 5, but outside prints 10?

Inside the function, $number is a new local variable set to 5 (see execution_table step 4 and 5). Outside, $number is the global variable still holding 10 (step 7). They are different variables.

Does the local $number inside the function change the global $number?

No, the local $number is separate and does not affect the global $number (see variable_tracker). The global $number remains 10 after the function call.

What if we want to change the global $number inside the function?

You must declare 'global $number;' inside the function to access and modify the global variable (not shown here). Without it, $number inside is local.

Visual Quiz - 3 Questions

Look at the execution_table, what value does $number have inside the function at step 4?

A undefined

B 10

C 5

D 0

💡 Hint

Check the 'Value' column for step 4 in execution_table.

At which step does the program print the global $number?

A Step 5

B Step 7

C Step 6

D Step 3

💡 Hint

Look for 'echo $number;' outside the function in execution_table.

If we add 'global $number;' inside the function before setting it, what would happen to the global $number?

A It changes to 5

B It stays 10

C It becomes undefined

D It causes an error

💡 Hint

Recall key_moments explanation about modifying global variables inside functions.

Concept Snapshot

Variable scope in PHP functions:
- Variables inside functions are local by default.
- Global variables are separate unless declared with 'global'.
- Local variables do not affect global variables.
- Use 'global $var;' inside functions to access global variables.
- Echo inside function prints local; outside prints global if names clash.

Full Transcript

This example shows how PHP handles variable scope in functions. A global variable named $number is set to 10. Inside the function test(), a new local variable $number is set to 5. When the function prints $number, it shows 5 because it uses the local variable. After the function ends, printing $number outside shows 10, the global variable. The local variable inside the function does not change the global one. To modify the global variable inside a function, you must declare it with 'global $number;'. This helps avoid confusion between local and global variables.