Compact and extract functions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using compact?

Consider the following PHP code snippet. What will be the output when it runs?

PHP

<?php
$name = 'Alice';
$age = 30;
$info = compact('name', 'age');
print_r($info);
?>

A Array ( [name] => 0 [age] => 0 )

B Array ( [0] => name [1] => age )

C Array ( [name] => 'name' [age] => 'age' )

D Array ( [name] => Alice [age] => 30 )

💡 Hint

The compact function creates an array using variable names as keys and their values as values.

The compact function takes variable names as strings and returns an associative array where keys are those names and values are the variables' values.

❓ Predict Output

intermediate

What does extract() do in this PHP code?

Look at this PHP code. What will be the output after running it?

PHP

<?php
$data = ['city' => 'Paris', 'country' => 'France'];
extract($data);
echo "$city, $country";
?>

A Paris, France

B city, country

C Array, Array

D Undefined variable error

💡 Hint

extract() creates variables from array keys with their corresponding values.

extract() takes keys from the array and creates variables with those names, assigning the array values to them.

🔧 Debug

advanced

Why does this extract() call cause a warning?

This PHP code produces a warning. What is the cause?

PHP

<?php
$info = ['name' => 'Bob', 'age' => 25];
extract($info, EXTR_PREFIX_SAME, 'dup');
echo "$name, $age, $dup_name";
?>

A Because $dup_name is not created if no conflict exists

B Because variables $name and $age already exist before extract()

C Because EXTR_PREFIX_SAME requires a prefix but none is given

D Because extract() cannot handle arrays with string keys

💡 Hint

EXTR_PREFIX_SAME adds prefix only if variable name conflicts with existing variables.

Since $name and $age do not exist before extract(), no conflict occurs, so no prefixed variables like $dup_name are created.

🧠 Conceptual

advanced

What happens if extract() is used with EXTR_SKIP and variables exist?

Given existing variables $a = 1 and $b = 2, and array ['a' => 10, 'b' => 20], what will be the values of $a and $b after extract() with EXTR_SKIP?

PHP

<?php
$a = 1;
$b = 2;
$arr = ['a' => 10, 'b' => 20];
extract($arr, EXTR_SKIP);
echo "$a, $b";
?>

A 10, 20

B 1, 2

C Undefined variable error

D 0, 0

💡 Hint

EXTR_SKIP prevents overwriting existing variables.

EXTR_SKIP tells extract() to skip variables that already exist, so $a and $b keep their original values.

❓ Predict Output

expert

What is the output of this combined compact and extract example?

Analyze this PHP code and determine the output printed.

PHP

<?php
$first = 'John';
$last = 'Doe';
$age = 40;
$person = compact('first', 'last');
extract($person);
$age = 50;
echo "$first $last is $age years old.";
?>

A John Doe is years old.

B John Doe is 40 years old.

C John Doe is 50 years old.

D Undefined variable error

💡 Hint

extract() creates variables from the compacted array, but $age is changed after extract().

compact() creates an array with 'first' and 'last'. extract() creates variables $first and $last. $age is not included in compact, so the later assignment $age = 50 is used in echo.