Array chunk and pad in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array_chunk with padding

What is the output of the following PHP code?

PHP

<?php
$array = [1, 2, 3, 4, 5];
$chunks = array_chunk($array, 2, true);
print_r($chunks);
?>

A Array ( [0] => Array ( [0] => 1 [1] => 2 ) [1] => Array ( [2] => 3 [3] => 4 ) )

B Array ( [0] => Array ( [0] => 1 [1] => 2 ) [1] => Array ( [0] => 3 [1] => 4 ) [2] => Array ( [0] => 5 ) )

C Array ( [0] => Array ( [0] => 1 [1] => 2 ) [1] => Array ( [2] => 3 [3] => 4 ) [2] => Array ( [0] => 5 ) )

D Array ( [0] => Array ( [0] => 1 [1] => 2 ) [1] => Array ( [2] => 3 [3] => 4 ) [2] => Array ( [4] => 5 ) )

💡 Hint

Remember that the third parameter true preserves keys in array_chunk.

When array_chunk is called with preserve_keys=true, the original keys are kept in each chunk. So the keys 0,1 remain in the first chunk, 2,3 in the second, and 4 in the last chunk.

❓ Predict Output

intermediate

Output of array_pad with negative size

What is the output of this PHP code snippet?

PHP

<?php
$array = [10, 20];
$padded = array_pad($array, -5, 0);
print_r($padded);
?>

A Array ( [0] => 0 [1] => 0 [2] => 0 [3] => 10 [4] => 20 )

B Fatal error: array_pad(): Size must be greater than zero

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

D Array ( [0] => 10 [1] => 20 [2] => 0 [3] => 0 [4] => 0 )

💡 Hint

Negative size pads at the beginning of the array.

array_pad with a negative size pads the array at the beginning until the array length reaches the absolute value of the size. So zeros are added before the original elements.

🔧 Debug

advanced

Identify the error in array_chunk usage

What error does this PHP code produce?

PHP

<?php
$array = [1, 2, 3, 4];
$chunks = array_chunk($array, 0);
print_r($chunks);
?>

A Array ( )

B Fatal error: array_chunk() expects parameter 2 to be integer, string given

C Warning: array_chunk(): Size parameter expected to be greater than 0

D No output, script runs silently

💡 Hint

Check the minimum allowed value for the size parameter in array_chunk.

array_chunk requires the size parameter to be a positive integer greater than zero. Passing zero triggers a warning.

❓ Predict Output

advanced

Result length after array_pad

How many elements does the array have after this code runs?

PHP

<?php
$array = [5, 6, 7];
$padded = array_pad($array, 6, 9);
echo count($padded);
?>

A 6

B 9

C 3

D Error

💡 Hint

array_pad extends the array to the specified size if needed.

array_pad adds elements to the array until its length matches the absolute value of the size parameter. Here, it pads from 3 to 6 elements.

🧠 Conceptual

expert

Understanding array_chunk with preserve_keys and array_pad combined

Given the code below, what is the output?

PHP

<?php
$array = [0 => 'a', 1 => 'b', 2 => 'c'];
$chunks = array_chunk($array, 2, true);
$chunks[1] = array_pad($chunks[1], 3, 'x');
print_r($chunks);
?>

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

B Array ( [0] => Array ( [0] => a [1] => b ) [1] => Array ( [2] => c [3] => x [4] => x ) )

C Array ( [0] => Array ( [0] => a [1] => b ) [1] => Array ( [2] => c [3] => x ) )

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

💡 Hint

array_chunk with preserve_keys keeps original keys; array_pad adds elements with numeric keys starting from 0.

array_chunk with preserve_keys keeps keys 0 and 1 in first chunk, 2 in second. array_pad pads the second chunk to length 3, adding elements with keys 3 and 4 because keys 0 and 1 are taken by original keys in chunk 1.