Array key and value extraction in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array_keys with numeric keys

What is the output of the following PHP code?

PHP

<?php
$array = [10 => 'a', 20 => 'b', 30 => 'c'];
print_r(array_keys($array));
?>

A Array ( [0] => 10 [1] => 20 [2] => 30 )

B Array ( [0] => a [1] => b [2] => c )

C Array ( [10] => 0 [20] => 1 [30] => 2 )

D Array ( [0] => 0 [1] => 1 [2] => 2 )

💡 Hint

array_keys returns the keys of the array, not the values.

array_keys returns an array containing all the keys from the input array. Here, the keys are 10, 20, and 30.

❓ Predict Output

intermediate

Output of array_values with associative keys

What will this PHP code output?

PHP

<?php
$array = ['x' => 100, 'y' => 200, 'z' => 300];
print_r(array_values($array));
?>

A Array ( [0] => 100 [1] => 200 [2] => 300 )

B Array ( [0] => x [1] => y [2] => z )

C Array ( [x] => 100 [y] => 200 [z] => 300 )

D Array ( [100] => 0 [200] => 1 [300] => 2 )

💡 Hint

array_values returns the values of the array, ignoring keys.

array_values returns an array of all the values from the input array, reindexing them with numeric keys starting at 0.

❓ Predict Output

advanced

Result of array_keys with search value

What does this PHP code output?

PHP

<?php
$array = ['a' => 1, 'b' => 2, 'c' => 1, 'd' => 3];
print_r(array_keys($array, 1));
?>

A Array ( )

B Array ( [0] => a [1] => c )

C Array ( [a] => 1 [c] => 1 )

D Array ( [0] => 1 [1] => 1 )

💡 Hint

array_keys can accept a second parameter to filter keys by value.

array_keys with a second parameter returns all keys that have the specified value. Here, keys 'a' and 'c' have value 1.

❓ Predict Output

advanced

Output of array_values on mixed keys

What is the output of this PHP code?

PHP

<?php
$array = [5 => 'apple', 'color' => 'red', 10 => 'banana'];
print_r(array_values($array));
?>

A Array ( [apple] => 0 [red] => 1 [banana] => 2 )

B Array ( [5] => apple [color] => red [10] => banana )

C Array ( [0] => 5 [1] => color [2] => 10 )

D Array ( [0] => apple [1] => red [2] => banana )

💡 Hint

array_values returns values reindexed with numeric keys starting at 0.

array_values returns all values from the array ignoring original keys and reindexes them starting at 0.

❓ Predict Output

expert

Count of keys returned by array_keys with strict search

What is the output of this PHP code?

PHP

<?php
$array = [0 => '0', 1 => 0, 2 => false, 3 => null];
$result = array_keys($array, 0, true);
echo count($result);
?>

A 2

B 3

C 1

D 4

💡 Hint

The third parameter in array_keys enforces strict type comparison.

With strict=true, only keys with value exactly equal to integer 0 are returned. Only key 1 has value 0 as integer. Others differ in type.