Multidimensional arrays in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of nested array access

What is the output of this PHP code?

PHP

<?php
$array = [[1, 2], [3, 4], [5, 6]];
echo $array[1][0];
?>

A 5

B 2

C 4

D 3

💡 Hint

Remember that arrays start at index 0.

The outer array has three elements: [0]=>[1,2], [1]=>[3,4], [2]=>[5,6]. Accessing $array[1] gives [3,4], and $array[1][0] is 3.

❓ Predict Output

intermediate

Count elements in multidimensional array

What is the output of this PHP code?

PHP

<?php
$array = [
  'fruits' => ['apple', 'banana'],
  'vegetables' => ['carrot', 'pea', 'corn']
];
echo count($array['vegetables']);
?>

A 5

B 2

C 3

D 1

💡 Hint

count() counts elements in the specified array.

The 'vegetables' array has three elements: 'carrot', 'pea', and 'corn'. So count($array['vegetables']) returns 3.

🔧 Debug

advanced

Identify the error in multidimensional array access

What error does this PHP code produce?

PHP

<?php
$array = [[1, 2], [3, 4]];
echo $array[2][0];
?>

A Undefined offset: 2

B Parse error: syntax error

C Fatal error: Cannot use [] for reading

D Notice: Undefined variable

💡 Hint

Check if the index exists before accessing.

The outer array has indexes 0 and 1 only. Accessing $array[2] causes an undefined offset error.

📝 Syntax

advanced

Which option correctly defines a multidimensional array?

Which of the following PHP code snippets correctly defines a multidimensional array with two rows and two columns?

A $array = [[1, 2], [3 4]];

B $array = [[1, 2], [3, 4]];

C $array = [1, 2; 3, 4];

D $array = array(1, 2, 3, 4);

💡 Hint

Look for proper array syntax and separators.

Option B uses correct PHP array syntax with nested arrays separated by commas. Option B uses semicolon inside array which is invalid. Option B is a flat array, not multidimensional. Option B misses a comma between 3 and 4.

🚀 Application

expert

Calculate sum of all elements in a multidimensional array

Given the multidimensional array below, what is the sum of all its integer elements?

PHP

<?php
$array = [
  [1, 2, 3],
  [4, 5],
  [6]
];
$sum = 0;
foreach ($array as $subarray) {
  foreach ($subarray as $value) {
    $sum += $value;
  }
}
echo $sum;
?>

A 21

B 20

C 18

D 19

💡 Hint

Add all numbers: 1+2+3+4+5+6.

The sum is 1+2+3+4+5+6 = 21.