Array access and modification in PHP - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to access the first element of the array.

PHP

<?php
$fruits = ['apple', 'banana', 'cherry'];
echo $fruits[[1]];
?>

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

A3

B1

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the first index instead of 0.

Using an index outside the array range.

The first element in a PHP array starts at index 0.

2fill in blank

medium

Complete the code to change the second element of the array to 'orange'.

PHP

<?php
$colors = ['red', 'green', 'blue'];
$colors[[1]] = 'orange';
print_r($colors);
?>

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

A1

B0

C2

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the wrong index.

Using an index that does not exist.

The second element has index 1, so we assign 'orange' to $colors[1].

3fill in blank

hard

Fix the error in the code to correctly add a new element 'pear' to the array.

PHP

<?php
$fruits = ['apple', 'banana'];
$fruits[1] = 'pear';
print_r($fruits);
?>

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

A[2]

B[3]

C[]

D(2)

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets.

Using an index that skips positions.

Using empty square brackets [] adds a new element at the next available index.

4fill in blank

hard

Fill both blanks to create an associative array with keys as names and values as ages.

PHP

<?php
$ages = [[1] => 25, [2] => 30];
print_r($ages);
?>

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

A'Alice'

B'Bob'

C'Charlie'

D'David'

Attempts:

3 left

💡 Hint

Common Mistakes

Using numbers as keys without quotes.

Forgetting quotes around string keys.

Keys in associative arrays are strings. Here, 'Alice' and 'Bob' are used as keys.

5fill in blank

hard

Fill all three blanks to create an array of squares for numbers greater than 3.

PHP

<?php
$numbers = [1, 2, 3, 4, 5];
$squares = [[1] => [2] for [3] in $numbers if [3] > 3];
print_r($squares);
?>

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

A$num

B$num * $num

C$number

D$number * $number

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Not squaring the number correctly.

We use $number as the variable name and square it with $number * $number for numbers greater than 3.

Practice

1. What is the correct way to access the first element of an array $arr in PHP?

easy

A. $arr{0}

B. $arr[1]

C. $arr[0]

D. $arr->0

Solution

1. Step 1: Understand PHP array indexing

   PHP arrays start at index 0, so the first element is at index 0.

2. Step 2: Identify correct syntax for array access

   Use square brackets with the index number: $arr[0].

3. Final Answer:

   $arr[0] -> Option C

4. Quick Check:

   First element index = 0 [OK]

Hint: First element is always at index 0 in PHP arrays [OK]

Common Mistakes:

• Using index 1 for first element
• Using curly braces for array access
• Using object property syntax

2. Which of the following is the correct way to change the value of the third element in array $arr to 10?

easy

A. $arr(3) = 10;

B. $arr[2] = 10;

C. $arr->2 = 10;

D. $arr{3} = 10;

Solution

1. Step 1: Identify the index of the third element

   Arrays start at 0, so the third element is at index 2.

2. Step 2: Use correct syntax to assign value

   Use square brackets with index 2: $arr[2] = 10;.

3. Final Answer:

   $arr[2] = 10; -> Option B

4. Quick Check:

   Index 2 for third element assignment [OK]

Hint: Use square brackets and zero-based index to modify array [OK]

Common Mistakes:

• Using parentheses instead of brackets
• Using object property syntax
• Using wrong index number

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

$arr = [5, 10, 15];
$arr[1] = $arr[1] + 5;
echo $arr[1];

medium

A. 15

B. 10

C. 20

D. 5

Solution

1. Step 1: Understand initial array values

   $arr = [5, 10, 15]; so $arr[1] is 10.

2. Step 2: Calculate new value of $arr[1]

   $arr[1] = $arr[1] + 5 means 10 + 5 = 15.

3. Final Answer:

   15 -> Option A

4. Quick Check:

   10 + 5 = 15 [OK]

Hint: Add to existing value using $arr[index] + number [OK]

Common Mistakes:

• Printing old value without update
• Adding index instead of value
• Confusing array indexes

4. Identify the error in the following PHP code snippet:

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

medium

A. Accessing an undefined index causes an error

B. Cannot echo array elements directly

C. Syntax error in array declaration

D. Assigning to index 3 adds a new element without error

Solution

1. Step 1: Check array indexes and assignment

   Array has indexes 0,1,2 initially. Assigning $arr[3] = 4 adds a new element at index 3.

2. Step 2: Confirm if this causes error

   PHP allows adding new elements by assigning to new indexes without error.

3. Final Answer:

   Assigning to index 3 adds a new element without error -> Option D

4. Quick Check:

   PHP arrays auto-expand on new index assignment [OK]

Hint: Assigning new index adds element; no error in PHP [OK]

Common Mistakes:

• Thinking accessing undefined index causes error
• Confusing syntax error with runtime behavior
• Believing echo can't print array elements

5. Given the array $arr = [2, 4, 6, 8];, which code snippet correctly doubles each element's value by modifying the array in place?

hard

A. for ($i = 0; $i < count($arr); $i++) { $arr[$i] *= 2; }

B. $arr = array_fill(0, count($arr), 2 * $arr[0]);

C. array_map(fn($v) => $v * 2, $arr);

D. foreach ($arr as $value) { $value = $value * 2; }

Solution

1. Step 1: Understand how to modify array elements in place

   Using a for loop with index allows direct modification of each element.

2. Step 2: Analyze each option

   A: foreach copies values, does not modify original array.
   B: array_fill replaces all elements with same value, incorrect.
   C: array_map returns new array, original unchanged.
   D: for loop modifies $arr[$i] directly.

3. Final Answer:

   for ($i = 0; $i < count($arr); $i++) { $arr[$i] *= 2; } -> Option A

4. Quick Check:

   Use indexed loop to modify array elements [OK]

Hint: Use for loop with indexes to change array elements directly [OK]

Common Mistakes:

• Modifying foreach loop variable instead of array
• Expecting array_map to change original array
• Using array_fill incorrectly