Global keyword behavior in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of modifying a global variable inside a function

What is the output of this PHP code?

PHP

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

A Error: Undefined variable

B 15

C 10

D 5

💡 Hint

Remember that the global keyword allows access to the variable outside the function.

The global keyword inside the function links $a to the global $a. So modifying $a inside the function changes the global variable. After calling test(), $a becomes 15.

❓ Predict Output

intermediate

Effect of missing global keyword on variable inside function

What will this PHP code output?

PHP

<?php
$x = 7;
function addFive() {
    $x = $x + 5;
    echo $x;
}
addFive();
echo $x;

A 7 7

B 12 7

C Error: Undefined variable $x

D 5 7

💡 Hint

Inside the function, $x is not declared global and is used before assignment.

Without the global keyword, $x inside addFive() is local. The right side $x is undefined (null, treated as 0), so $x = 5, echoes 5 (with notice). Global $x remains 7, outputs "57".

🔧 Debug

advanced

Why does this code not update the global variable?

This PHP code tries to update a global variable inside a function but fails. Why?

PHP

<?php
$count = 0;
function increment() {
    $count++;
}
increment();
echo $count;

A Because $count is not declared global inside the function, so local $count is incremented but global remains 0.

B Because $count is a constant and cannot be changed.

C Because increment() is never called.

D Because PHP does not allow modifying global variables inside functions.

💡 Hint

Check if the function has access to the global variable.

Without the global keyword, $count inside the function is local and uninitialized, so incrementing it does not affect the global $count.

📝 Syntax

advanced

Identify the syntax error related to global keyword

Which option contains a syntax error in using the global keyword?

A function foo() { global $var; $var = 10; }

B function foo() { global $var; echo $var; }

C function foo() { global var; var = 10; }

D function foo() { global $var; $var += 5; }

💡 Hint

Check if the variable name after global has the correct syntax.

In PHP, the global keyword must be followed by a variable name with a $ sign. Option C misses the $ sign, causing a syntax error.

🚀 Application

expert

How many items are in the global array after function call?

Consider this PHP code. How many elements does the global array $data have after calling updateData()?

PHP

<?php
$data = [1, 2, 3];
function updateData() {
    global $data;
    $data[] = 4;
    $data = array_unique($data);
}
updateData();

A 4

B 3

C 1

D 0

💡 Hint

The function adds a new element and then removes duplicates.

The function adds 4 to the global array $data, then removes duplicates. Since 4 is new, the array has 4 elements after the call.