Multidimensional arrays in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a multidimensional array in PHP?

A multidimensional array is an array that contains one or more arrays inside it. It is like a table or grid where each element can be accessed using multiple keys or indexes.

beginner

How do you access the element 'PHP' in this array?<br>

$arr = [['HTML', 'CSS'], ['JavaScript', 'PHP']];

You access 'PHP' by using two indexes: $arr[1][1]. The first index selects the second array, and the second index selects the second element inside it.

intermediate

How to add a new element 'Python' to the second array in a multidimensional array?

Use $arr[1][] = 'Python'; to add 'Python' at the end of the second array inside the multidimensional array.

beginner

What will count($arr) return if $arr = [[1,2], [3,4], [5,6]];?

It will return 3 because count() counts the number of elements in the outer array, which has three inner arrays.

intermediate

How can you loop through all elements in a multidimensional array?

Use nested foreach loops: the outer loop goes through each inner array, and the inner loop goes through each element inside those arrays.

What does $arr[0][1] access in a multidimensional array?

A The first element of the second inner array

B The first element of the first inner array

C The second element of the first inner array

D The second element of the second inner array

$arr[0] selects the first inner array, and [1] selects its second element.

How do you add a new inner array to a multidimensional array $arr?

A <code>$arr[] = ['new', 'array'];</code>

B <code>$arr = ['new', 'array'];</code>

C <code>$arr[0][] = 'new';</code>

D <code>array_push($arr[0], ['new', 'array']);</code>

Using $arr[] = [...] adds a new inner array at the end of the outer array.

What will count($arr, COUNT_RECURSIVE) do?

A Count all elements including those in inner arrays

B Count only the outer array elements

C Count only the inner array elements

D Cause an error

Using COUNT_RECURSIVE counts all elements inside all nested arrays.

Which loop structure is best to iterate over a multidimensional array?

A While loop only

B Nested foreach loops

C Single for loop

D Do-while loop only

Nested foreach loops let you access each inner array and its elements easily.

What type of data structure is a multidimensional array similar to?

A Queue only

B Single list

C Stack only

D Table or grid

Multidimensional arrays are like tables with rows and columns.

Explain what a multidimensional array is and how you access its elements in PHP.

Think of it like a table with rows and columns.

Describe how to loop through all elements of a multidimensional array and why nested loops are needed.

Imagine opening each box inside a bigger box.