Array push and pop in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the array_push() function do in PHP?

It adds one or more elements to the end of an array, increasing its size by the number of elements added.

beginner

What does the array_pop() function do in PHP?

It removes the last element from an array and returns that element, reducing the array size by one.

beginner

How do array_push() and array_pop() relate to a real-life stack of plates?

Adding a plate on top is like array_push(), and taking the top plate off is like array_pop(). Both work with the last item added.

intermediate

What happens if you use array_pop() on an empty array?

It returns NULL because there is no element to remove.

intermediate

Can array_push() add multiple elements at once? How?

Yes, by passing multiple values as additional arguments after the array, like array_push($arr, 'a', 'b', 'c').

What does array_pop() return when called on a non-empty array?

A The last element of the array

B The first element of the array

C The entire array

D NULL

array_pop() removes and returns the last element of the array.

Which function adds elements to the end of an array in PHP?

A array_push()

B array_pop()

C array_shift()

D array_unshift()

array_push() adds elements to the end of an array.

What will array_pop() return if the array is empty?

A An error

B NULL

C Zero

D The first element

If the array is empty, array_pop() returns NULL.

How can you add multiple elements to an array at once using array_push()?

A By calling <code>array_push()</code> multiple times

B By using a loop inside <code>array_push()</code>

C By passing multiple elements as arguments in one call

D You cannot add multiple elements at once

You can pass multiple elements as additional arguments to array_push() to add them all at once.

Which of these is a correct way to add 'apple' and 'banana' to the array $fruits?

A array_pop('apple', 'banana', $fruits);

B array_pop($fruits, 'apple', 'banana');

C array_push('apple', 'banana', $fruits);

D array_push($fruits, 'apple', 'banana');

array_push($fruits, 'apple', 'banana'); correctly adds both elements to the array.

Explain how array_push() and array_pop() work in PHP and give a real-life example.

Think about adding and removing plates from a stack.

What happens if you call array_pop() on an empty array? Why is this behavior useful?

Consider what happens when you try to take something from an empty box.

Practice

1. What does the PHP function array_push do to an array?

easy

A. Adds one or more elements to the end of the array

B. Removes the first element from the array

C. Removes the last element from the array

D. Sorts the array in ascending order

Solution

1. Step 1: Understand the purpose of array_push

   array_push is used to add elements to the end of an existing array.

2. Step 2: Compare with other array functions

   Functions like array_pop remove elements, but array_push only adds elements at the end.

3. Final Answer:

   Adds one or more elements to the end of the array -> Option A

4. Quick Check:

   array_push = add elements at end [OK]

Hint: Remember: push means add at the end [OK]

Common Mistakes:

• Confusing array_push with array_pop
• Thinking array_push removes elements
• Assuming array_push sorts the array

2. Which of the following is the correct syntax to add an element 'apple' to the array $fruits using array_push?

easy

A. array_push('apple', $fruits);

B. array_push($fruits['apple']);

C. array_push($fruits => 'apple');

D. array_push($fruits, 'apple');

Solution

1. Step 1: Recall the function signature

   The correct syntax is array_push(array, value1, value2, ...), where the first argument is the array variable.

2. Step 2: Check each option

   array_push($fruits, 'apple'); correctly uses array_push($fruits, 'apple');. Others misuse argument order or syntax.

3. Final Answer:

   array_push($fruits, 'apple'); -> Option D

4. Quick Check:

   array_push(array, value) syntax [OK]

Hint: First argument is array, then values to add [OK]

Common Mistakes:

• Swapping argument order
• Using arrow => instead of comma
• Passing only one argument incorrectly

3. What will be the output of the following PHP code?

$colors = ['red', 'green'];
array_push($colors, 'blue');
$last = array_pop($colors);
print_r($colors);
echo $last;

medium

A. Array ( [0] => red [1] => green [2] => blue ) blue

B. Array ( [0] => red [1] => green ) blue

C. Array ( [0] => red [1] => green ) green

D. Array ( [0] => red [1] => green [2] => blue ) green

Solution

1. Step 1: Understand array_push effect

   array_push adds 'blue' to the end, so array becomes ['red', 'green', 'blue'].

2. Step 2: Understand array_pop effect

   array_pop removes and returns the last element 'blue', so array becomes ['red', 'green'] and $last = 'blue'.

3. Final Answer:

   Array ( [0] => red [1] => green ) blue -> Option B

4. Quick Check:

   push adds, pop removes last [OK]

Hint: Push adds last, pop removes last [OK]

Common Mistakes:

• Thinking pop removes first element
• Expecting array to still have 'blue'
• Confusing printed array and echoed value

4. Identify the error in the following PHP code snippet:

$numbers = [1, 2, 3];
array_pop($numbers, 2);
print_r($numbers);

medium

A. No error, code works fine

B. array_pop should be called before array initialization

C. array_pop accepts only one argument, extra argument causes error

D. array_pop cannot be used on numeric arrays

Solution

1. Step 1: Check array_pop function signature

   array_pop accepts only one argument: the array variable.

2. Step 2: Analyze the code

   Passing a second argument (2) is invalid and will cause an error.

3. Final Answer:

   array_pop accepts only one argument, extra argument causes error -> Option C

4. Quick Check:

   array_pop(array) only one argument [OK]

Hint: array_pop takes exactly one argument [OK]

Common Mistakes:

• Passing multiple arguments to array_pop
• Thinking array_pop removes multiple elements
• Assuming no error on extra arguments

5. Given an empty array $stack = [];, which sequence of PHP statements correctly adds 'first', 'second', then removes the last added element and stores it in $removed?

hard

A. array_push($stack, 'first'); array_push($stack, 'second'); $removed = array_pop($stack);

B. $removed = array_pop($stack); array_push($stack, 'first'); array_push($stack, 'second');

C. array_pop($stack, 'first'); array_pop($stack, 'second'); $removed = array_push($stack);

D. array_push('first', $stack); array_push('second', $stack); $removed = array_pop($stack);

Solution

1. Step 1: Add elements in correct order

   Use array_push($stack, 'first') and then array_push($stack, 'second') to add elements to the stack.

2. Step 2: Remove last element and store it

   Use $removed = array_pop($stack); to remove and save the last added element ('second').

3. Final Answer:

   array_push($stack, 'first'); array_push($stack, 'second'); $removed = array_pop($stack); -> Option A

4. Quick Check:

   Push adds, pop removes last [OK]

Hint: Push then pop to simulate stack behavior [OK]

Common Mistakes:

• Calling array_pop before pushing elements
• Passing arguments in wrong order
• Using array_pop with extra arguments