Array sort functions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using sort()?

Consider the following PHP code snippet. What will be the output after sorting the array with sort()?

PHP

<?php
$arr = [3, 1, 4, 1, 5];
sort($arr);
print_r($arr);
?>

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

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

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

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

💡 Hint

sort() sorts the array in ascending order and reindexes the keys.

The sort() function sorts the array in ascending order and resets the keys starting from 0. So the array becomes [1, 1, 3, 4, 5].

❓ Predict Output

intermediate

What is the output of this PHP code using asort()?

Look at this PHP code. What will be printed after using asort() on the array?

PHP

<?php
$arr = [3 => 'apple', 1 => 'banana', 2 => 'cherry'];
asort($arr);
print_r($arr);
?>

A Array ( [3] => apple [2] => cherry [1] => banana )

B Array ( [1] => banana [3] => apple [2] => cherry )

C Array ( [3] => apple [1] => banana [2] => cherry )

D Array ( [2] => cherry [1] => banana [3] => apple )

💡 Hint

asort() sorts values but keeps original keys.

asort() sorts the array by values in ascending order but preserves the original keys. Since 'apple' < 'banana' < 'cherry', the order is apple, banana, cherry with keys 3,1,2 respectively.

❓ Predict Output

advanced

What is the output of this PHP code using krsort()?

What will be the output after sorting the array by keys in descending order using krsort()?

PHP

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

A Array ( [b] => 2 [c] => 1 [a] => 3 )

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

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

D Array ( [c] => 1 [b] => 2 [a] => 3 )

💡 Hint

krsort() sorts keys in reverse (descending) order.

krsort() sorts the array by keys in descending order. The keys 'c', 'b', 'a' sorted descending are 'c', 'b', 'a'. Values stay with their keys.

❓ Predict Output

advanced

What error does this PHP code raise when using usort() incorrectly?

What error will this PHP code produce?

PHP

<?php
$arr = [3, 1, 4];
usort($arr, 'nonexistent_function');
print_r($arr);
?>

A Warning: usort() expects parameter 2 to be a valid callback, function 'nonexistent_function' not found

B Fatal error: Call to undefined function nonexistent_function()

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

D Parse error: syntax error, unexpected 'usort'

💡 Hint

usort() requires a valid callback function name as second argument.

usort() tries to call the callback function 'nonexistent_function' which does not exist, so PHP issues a warning about invalid callback.

🧠 Conceptual

expert

How many items are in the array after this PHP code runs?

Given this PHP code, how many items will the array contain after sorting?

PHP

<?php
$arr = [0 => 'zero', 1 => 'one', 2 => 'two'];
array_splice($arr, 1, 1);
sort($arr);
print_r($arr);
?>

A 2

B 3

C 1

D 0

💡 Hint

array_splice removes one element at index 1, then sort reindexes the array.

array_splice removes the element at index 1 ('one'), so the array has 2 elements left. sort() then sorts and reindexes the array with 2 items.