Multidimensional arrays in PHP - Mini Project: Build & Apply

Working with Multidimensional Arrays in PHP

📖 Scenario: You are managing a small library system. You want to store information about books, including their title, author, and year published. This information will be stored in a multidimensional array.

🎯 Goal: Create a multidimensional array to hold book information, add a new book, retrieve specific book details, and display the list of books.

📋 What You'll Learn

Create a multidimensional array called library with three books, each book having keys title, author, and year.

Add a new book to the library array.

Use a foreach loop to iterate over the library array and access each book's details.

Print the details of each book in a readable format.

💡 Why This Matters

🌍 Real World

Multidimensional arrays are useful to store and organize complex data like records, tables, or objects in many applications such as libraries, inventories, or user profiles.

💼 Career

Understanding multidimensional arrays is essential for backend developers, data analysts, and anyone working with structured data in PHP or similar languages.

1

Create the initial multidimensional array

Create a multidimensional array called library with these exact three books:
[ 'title' => '1984', 'author' => 'George Orwell', 'year' => 1949 ],
[ 'title' => 'To Kill a Mockingbird', 'author' => 'Harper Lee', 'year' => 1960 ],
[ 'title' => 'The Great Gatsby', 'author' => 'F. Scott Fitzgerald', 'year' => 1925 ].

PHP

# Create the multidimensional array called library
# Your code here

Hint

Remember to use an array of arrays, where each inner array holds keys 'title', 'author', and 'year'.

2

Add a new book to the library

Add a new book to the library array with these details:
'title' => 'Pride and Prejudice', 'author' => 'Jane Austen', 'year' => 1813.

PHP

 '1984', 'author' => 'George Orwell', 'year' => 1949 ],
    [ 'title' => 'To Kill a Mockingbird', 'author' => 'Harper Lee', 'year' => 1960 ],
    [ 'title' => 'The Great Gatsby', 'author' => 'F. Scott Fitzgerald', 'year' => 1925 ]
];

# Add the new book to the library array
# Your code here

Hint

Use the array append syntax $library[] = to add the new book.

3

Loop through the library to access book details

Use a foreach loop with variables $book to iterate over the $library array and access each book's details.

PHP

 '1984', 'author' => 'George Orwell', 'year' => 1949 ],
    [ 'title' => 'To Kill a Mockingbird', 'author' => 'Harper Lee', 'year' => 1960 ],
    [ 'title' => 'The Great Gatsby', 'author' => 'F. Scott Fitzgerald', 'year' => 1925 ]
];

$library[] = [ 'title' => 'Pride and Prejudice', 'author' => 'Jane Austen', 'year' => 1813 ];

# Use a foreach loop to access each book's details
# Your code here

Hint

Use foreach ($library as $book) to loop through each book array.

4

Print the details of each book

Inside the foreach loop, print each book's title, author, and year in this format:
Title: [title], Author: [author], Year: [year].
Use echo to display the output.

PHP

 '1984', 'author' => 'George Orwell', 'year' => 1949 ],
    [ 'title' => 'To Kill a Mockingbird', 'author' => 'Harper Lee', 'year' => 1960 ],
    [ 'title' => 'The Great Gatsby', 'author' => 'F. Scott Fitzgerald', 'year' => 1925 ]
];

$library[] = [ 'title' => 'Pride and Prejudice', 'author' => 'Jane Austen', 'year' => 1813 ];

foreach ($library as $book) {
    # Print the book details here
    # Your code here
}

Hint

Use echo with double quotes and curly braces to insert array values inside the string.

Practice

1. What is a multidimensional array in PHP?

easy

A. An array containing one or more arrays inside it

B. An array with only string keys

C. An array that can only hold numbers

D. An array that cannot be changed after creation

Solution

1. Step 1: Understand array nesting

   A multidimensional array is an array that contains other arrays as its elements.

2. Step 2: Identify the correct definition

   An array containing one or more arrays inside it correctly describes this nesting, while others describe unrelated properties.

3. Final Answer:

   An array containing one or more arrays inside it -> Option A

4. Quick Check:

   Multidimensional array = nested arrays [OK]

Hint: Think of arrays inside arrays like boxes within boxes [OK]

Common Mistakes:

• Confusing multidimensional arrays with simple arrays
• Thinking keys must be strings only
• Believing arrays cannot be changed

2. Which of the following is the correct way to access the element 'blue' in this array?

$colors = [['red', 'green'], ['blue', 'yellow']];

easy

A. $colors[1][0]

B. $colors[0][2]

C. $colors[2][1]

D. $colors[1][1]

Solution

1. Step 1: Identify the position of 'blue'

   'blue' is in the second inner array (index 1) and is the first element (index 0) there.

2. Step 2: Use correct indices to access

   Accessing $colors[1][0] retrieves 'blue'. Other options point to wrong indices or elements.

3. Final Answer:

   $colors[1][0] -> Option A

4. Quick Check:

   Second array, first element = 'blue' [OK]

Hint: Count arrays and elements starting at zero [OK]

Common Mistakes:

• Using wrong index numbers
• Confusing first and second arrays
• Trying to access non-existing elements

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

$matrix = [[1, 2], [3, 4]];
echo $matrix[0][1] + $matrix[1][0];

medium

A. 9

B. 7

C. 5

D. Error

Solution

1. Step 1: Identify the values at given indices

   $matrix[0][1] is 2 and $matrix[1][0] is 3.

2. Step 2: Calculate the sum

   2 + 3 equals 5, so the output is 5.

3. Final Answer:

   5 -> Option C

4. Quick Check:

   2 + 3 = 5 [OK]

Hint: Add values at given indices carefully [OK]

Common Mistakes:

• Mixing up indices
• Adding wrong elements
• Expecting string output

4. Find the error in this code snippet:

$arr = [[1, 2], [3, 4];
echo $arr[1][1];

medium

A. Missing closing bracket for the first array

B. Missing closing bracket for the outer array

C. Incorrect index used to access element

D. Missing semicolon after echo statement

Solution

1. Step 1: Check array syntax

   The array starts with [[ but only one closing bracket ] is present before the semicolon.

2. Step 2: Identify missing bracket

   The outer array requires a closing bracket ], so the code should end with ]];

3. Final Answer:

   Missing closing bracket for the outer array -> Option B

4. Quick Check:

   Outer array brackets must match [OK]

Hint: Count opening and closing brackets carefully [OK]

Common Mistakes:

• Confusing inner and outer brackets
• Ignoring syntax errors
• Assuming semicolon fixes bracket issues

5. Given this multidimensional array representing students and their scores:
<pre>$students = [
['name' => 'Alice', 'scores' => [85, 90]],
['name' => 'Bob', 'scores' => [78, 82]],
['name' => 'Charlie', 'scores' => [92, 88]]
];

Which code correctly calculates and prints the average score of Bob?

hard

A. $avg = array_sum($students[2]['scores']) / count($students[2]['scores']);echo $avg;

B. $avg = array_sum($students['Bob']['scores']) / count($students['Bob']['scores']);echo $avg;

C. $avg = array_sum($students[1]['score']) / count($students[1]['score']);echo $avg;

D. $avg = array_sum($students[1]['scores']) / count($students[1]['scores']);echo $avg;

Solution

1. Step 1: Locate Bob's data in the array

   Bob is at index 1, and his scores are under the key 'scores'.

2. Step 2: Calculate average correctly

   Use array_sum and count on $students[1]['scores'] to get average. $avg = array_sum($students[1]['scores']) / count($students[1]['scores']);
   echo $avg; does this correctly.

3. Final Answer:

   $avg = array_sum($students[1]['scores']) / count($students[1]['scores']); echo $avg; -> Option D

4. Quick Check:

   Index 1 and 'scores' key used correctly [OK]

Hint: Use numeric index for array, string keys for inner arrays [OK]

Common Mistakes:

• Using string key for outer array
• Misspelling 'scores' key
• Using wrong index for Bob