Array push and pop in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using array_push and array_pop?

Consider the following PHP code:

$fruits = ['apple', 'banana'];
array_push($fruits, 'cherry');
$popped = array_pop($fruits);
echo $popped . ', ' . implode(', ', $fruits);

What will be printed?

PHP

$fruits = ['apple', 'banana'];
array_push($fruits, 'cherry');
$popped = array_pop($fruits);
echo $popped . ', ' . implode(', ', $fruits);

A cherry, apple, banana

B cherry, apple, banana, cherry

C herry, apple, banana

D ananab ,elppa ,yrrehc

💡 Hint

Remember that array_pop removes the last element and returns it.

The array_push adds 'cherry' to the end of the array. Then array_pop removes and returns 'cherry'. So $popped is 'cherry', and the remaining array is ['apple', 'banana'].

❓ Predict Output

intermediate

What is the final array after these push and pop operations?

Given this PHP code:

$numbers = [1, 2, 3];
array_push($numbers, 4);
array_pop($numbers);
array_push($numbers, 5);
array_pop($numbers);
array_push($numbers, 6);
print_r($numbers);

What will print_r output?

PHP

$numbers = [1, 2, 3];
array_push($numbers, 4);
array_pop($numbers);
array_push($numbers, 5);
array_pop($numbers);
array_push($numbers, 6);
print_r($numbers);

A

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

B

Array
(
    [0] => 6
)

C

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 4
    [4] => 5
    [5] => 6
)

D

Array
(
    [0] => 1
    [1] => 2
    [2] => 3
    [3] => 6
)

💡 Hint

Each array_pop removes the last element added.

After pushing 4, array is [1,2,3,4]. Pop removes 4. Push 5, array is [1,2,3,5]. Pop removes 5. Push 6, array is [1,2,3,6].

❓ Predict Output

advanced

What does this PHP code output when mixing array_push with multiple values?

Look at this PHP code:

$colors = ['red'];
array_push($colors, 'green', 'blue');
$popped = array_pop($colors);
echo $popped . ', ' . implode(', ', $colors);

What will be printed?

PHP

$colors = ['red'];
array_push($colors, 'green', 'blue');
$popped = array_pop($colors);
echo $popped . ', ' . implode(', ', $colors);

A blue, red, green

B green, red, blue

C blue, red, green, blue

D green, red

💡 Hint

array_push can add multiple elements at once. array_pop removes the last element.

After pushing 'green' and 'blue', array is ['red', 'green', 'blue']. array_pop removes 'blue'. So $popped is 'blue', and array is ['red', 'green'].

❓ Predict Output

advanced

What error or output does this PHP code produce?

Analyze this PHP code:

$items = [];
$popped = array_pop($items);
echo $popped === null ? 'null' : $popped;

What will be printed?

PHP

$items = [];
$popped = array_pop($items);
echo $popped === null ? 'null' : $popped;

A Warning: array_pop() expects parameter 1 to be array, null given

B null

C Empty string

D 0

💡 Hint

What happens when you pop from an empty array?

array_pop returns null if the array is empty. No error is raised.

🧠 Conceptual

expert

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

Consider this PHP code snippet:

$stack = [];
array_push($stack, 'a');
array_push($stack, 'b', 'c');
array_pop($stack);
array_push($stack, 'd');
array_pop($stack);
array_pop($stack);

How many elements remain in $stack after all operations?

A 3

B 2

C 1

D 0

💡 Hint

Count carefully each push and pop step.

Step by step:
Start: []
Push 'a': ['a']
Push 'b', 'c': ['a','b','c']
Pop removes 'c': ['a','b']
Push 'd': ['a','b','d']
Pop removes 'd': ['a','b']
Pop removes 'b': ['a']
So 1 element remains.