Multidimensional arrays in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a 2D array with two rows.

PHP

<?php
$matrix = array(
    array(1, 2),
    [1]
);
print_r($matrix);
?>

Drag options to blanks, or click blank then click option'

Aarray(3, 4)

Barray(7, 8)

Carray(5, 6)

Darray(9, 10)

Attempts:

3 left

💡 Hint

Common Mistakes

Using a single value instead of an array for the second row.

Forgetting to use the array() function for the second row.

The second row of the 2D array is created with array(5, 6).

2fill in blank

medium

Complete the code to access the element '8' from the 2D array.

PHP

<?php
$matrix = array(
    array(1, 2, 3),
    array(4, 5, 6),
    array(7, 8, 9)
);
echo $matrix[1];
?>

Drag options to blanks, or click blank then click option'

A[2][1]

B[1][2]

C[0][2]

D[2][2]

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up row and column indexes.

Using 1-based indexes instead of 0-based.

The element '8' is in the third row (index 2) and second column (index 1), so $matrix[2][1] accesses it.

3fill in blank

hard

Fix the error in the code to correctly add a new row to the multidimensional array.

PHP

<?php
$matrix = array(
    array(1, 2),
    array(3, 4)
);
$matrix[] = [1];
print_r($matrix);
?>

Drag options to blanks, or click blank then click option'

Aarray(5, 6)

B5, 6

C[5, 6]

D"5, 6"

Attempts:

3 left

💡 Hint

Common Mistakes

Adding values without wrapping them in array().

Using string instead of array for the new row.

To add a new row, you must add an array. So array(5, 6) is correct.

4fill in blank

hard

Fill both blanks to create a 3x3 matrix with all zeros.

PHP

<?php
$matrix = array(
    array([1], [2], 0),
    array(0, 0, 0),
    array(0, 0, 0)
);
print_r($matrix);
?>

Drag options to blanks, or click blank then click option'

A0

B1

Cnull

D"0"

Attempts:

3 left

💡 Hint

Common Mistakes

Using string "0" instead of integer 0.

Using 1 or null instead of 0.

To create a matrix with all zeros, use 0 for each element.

5fill in blank

hard

Fill all three blanks to create an associative multidimensional array representing students and their scores.

PHP

<?php
$students = array(
    "Alice" => array("Math" => [1], "Science" => [2]),
    "Bob" => array("Math" => [3], "Science" => 85)
);
print_r($students);
?>

Drag options to blanks, or click blank then click option'

A90

B80

C75

D95

Attempts:

3 left

💡 Hint

Common Mistakes

Using strings instead of numbers for scores.

Mixing up scores between students or subjects.

Alice's Math score is 95, Science is 80, and Bob's Math score is 75.

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