array_shift() and array_unshift()

PHP course · Beginner · Lesson 60/116

Learn to remove from the start with array_shift() and add to the start with array_unshift().

array_shift() and array_unshift()

array_shift() removes the first element of an array and returns it. The remaining elements are re-indexed. For example, on $q = ["Ali", "Ayşe"];, array_shift($q) returns "Ali" and $q becomes ["Ayşe"].

array_unshift() adds one or more elements to the start. array_unshift($q, "Veli") puts "Veli" at the front. Together they form a queue: the first item in is the first one out.

Not a stack, a queue

array_shift() and array_unshift() form a queue pattern. In a queue, the first item added is the first one processed; this is called FIFO (first in, first out).

They are not the same as array_push() and array_pop(): push/pop work on the end of the array, while shift/unshift work on the start. Also, array_shift() returns the removed element, while array_unshift() returns the new count.

Exercise Build a queue and shift from the start

Define a $queue array and start it empty []. Use array_unshift() to add three values to the start in one call, in this order: "Alex", "Maya", "Sam". Then use array_shift() to assign the first element to $first and print it with echo $first . "\n".

Show example solution

First add with array_unshift($queue, "Alex", "Maya", "Sam");. Then take the first with $first = array_shift($queue); and print echo $first . "\n";.
Example solution:
<?php
$queue = [];
// Add to the queue, take the first and print
array_unshift($queue, "Alex", "Maya", "Sam");
$first = array_shift($queue);
echo $first . "\n";

Test yourself

What is the output of the code below?
```
$names = ["Ali", "Ayşe", "Mehmet"];
$first = array_shift($names);
echo $first;
```
- Ali
- Ayşe
- Mehmet
- null
Show answer

Ali — Correct. array_shift returns the first element; that is 'Ali'.

Write the function to add to the start

$queue = ["Ali", "Ayşe"];
____($queue, "Veli");
print_r($queue);

Show answer

$queue = ["Ali", "Ayşe"];
array_unshift($queue, "Veli");
print_r($queue);

Match each function to its end

array_push

Adds to the end
array_pop

Removes from the end
array_shift

Removes from the start
array_unshift

Adds to the start
What does array_unshift return?
- The removed item
- The first item
- The added item
- The new count
Show answer

The new count — Correct. array_unshift returns the new count.

array_shift() and array_unshift()