Global keyword behavior in PHP - Step-by-Step Execution

Concept Flow - Global keyword behavior

Start

↓

Define global variable

↓

Enter function

↓

Use 'global' keyword

↓

Access/modify global variable

↓

Exit function

↓

Global variable updated

↓

End

This flow shows how a global variable is defined outside a function, then accessed and modified inside a function using the 'global' keyword.

Execution Sample

PHP

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

This code defines a global variable $x, modifies it inside a function using 'global', then prints the updated value.

Execution Table

Step	Action	Variable	Value	Notes
1	Define global variable	$x	5	Global scope
2	Call function test()	-	-	Enter function scope
3	Declare 'global $x' inside function	$x	5	Link local $x to global $x
4	Assign $x = 10 inside function	$x	10	Modifies global $x
5	Exit function test()	-	-	Return to global scope
6	Echo $x	$x	10	Prints updated global variable

💡 Function ends and global variable $x is updated to 10

Variable Tracker

Variable	Start	After function call	Final
$x	5	10	10

Key Moments - 2 Insights

Why does $x inside the function change the global $x?

Because of the 'global $x;' declaration inside the function (see step 3 in execution_table), the local $x refers to the global $x, so modifying it changes the global variable.

What happens if we don't use 'global' inside the function?

Without 'global', $x inside the function is a new local variable, so changes won't affect the global $x (not shown in table but implied).

Visual Quiz - 3 Questions

Look at the execution table, what is the value of $x after step 4 inside the function?

A 10

B 5

C Undefined

D 0

💡 Hint

Check the 'Value' column at step 4 where $x is assigned 10 inside the function.

At which step does the global variable $x get updated?

A Step 2

B Step 3

C Step 4

D Step 6

💡 Hint

Look at the 'Action' and 'Notes' columns around step 4 where $x is assigned 10.

If we remove 'global $x;' from the function, what would be the output at step 6?

A 10

B 5

C Error

D 0

💡 Hint

Without 'global', the function modifies a local $x, so global $x remains unchanged as shown in variable_tracker.

Concept Snapshot

PHP 'global' keyword:
- Declares variables inside functions as global.
- Allows access and modification of global variables.
- Without 'global', variables inside functions are local.
- Changes to global variables persist after function ends.

Full Transcript

This example shows how PHP's 'global' keyword works. We start by defining a global variable $x with value 5. When we enter the function test(), we declare 'global $x;' which links the local $x to the global one. Then we assign 10 to $x inside the function, which updates the global variable. After the function ends, printing $x shows 10, confirming the global variable was changed. Without 'global', the function would only change a local copy, leaving the global $x unchanged.