Why array functions matter in PHP - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the number of elements in the array.

PHP

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

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

Acount

Bstrlen

Csizeof

Darray_length

Attempts:

3 left

💡 Hint

Common Mistakes

Using strlen() which counts string length, not array elements.

Using array_length which is not a PHP function.

The count() function returns the number of elements in an array.

2fill in blank

medium

Complete the code to add a new element 'orange' to the end of the array.

PHP

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

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

Ashift

Bpop

Cpush

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_pop() which removes the last element.

Using array_shift() which removes the first element.

The array_push() function adds one or more elements to the end of an array.

3fill in blank

hard

Fix the error in the code to check if 'banana' is in the array.

PHP

<?php
$fruits = ['apple', 'banana', 'cherry'];
if ([1]('banana', $fruits)) {
    echo 'Found banana';
} else {
    echo 'Banana not found';
}
?>

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

Aarray_key_exists

Bin_array

Carray_search

Disset

Attempts:

3 left

💡 Hint

Common Mistakes

Using array_key_exists which checks keys, not values.

Using isset which checks if a variable is set.

The in_array() function checks if a value exists in an array and returns true or false.

4fill in blank

hard

Fill both blanks to create an array of squares for numbers 1 to 5.

PHP

<?php
$numbers = [1, 2, 3, 4, 5];
$squares = array_map(function([1]) {
    return [2] * [1];
}, $numbers);
print_r($squares);
?>

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

A$n

C$num

D$number

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inside and outside the function argument.

Forgetting to multiply the variable by itself.

The anonymous function takes each number as $n and returns its square by multiplying $n * $n.

5fill in blank

hard

Fill all three blanks to filter numbers greater than 3 and create a new array with those numbers doubled.

PHP

<?php
$nums = [1, 2, 3, 4, 5];
$filtered = array_filter($nums, function([1]) {
    return [2] > 3;
});
$doubled = array_map(function([3]) {
    return [3] * 2;
}, $filtered);
print_r($doubled);
?>

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

A$num

C$n

D$val

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently inside the functions.

Not returning the correct condition in the filter function.

The filter function uses $num to check if the number is greater than 3. The map function uses $n to double each filtered number.

Practice

1. Why are PHP array functions important when working with lists?

easy

A. They make PHP run faster by changing the language core.

B. They simplify tasks like sorting and searching in arrays.

C. They allow arrays to store only numbers.

D. They prevent errors by disabling user input.

Solution

1. Step 1: Understand the role of array functions

   Array functions provide ready-made tools to handle common tasks like sorting, searching, and counting elements in arrays.

2. Step 2: Compare options

   Only They simplify tasks like sorting and searching in arrays. correctly states that array functions simplify tasks with arrays. Other options describe unrelated or incorrect effects.

3. Final Answer:

   They simplify tasks like sorting and searching in arrays. -> Option B

4. Quick Check:

   Array functions simplify array tasks = A [OK]

Hint: Remember: array functions make list tasks easier [OK]

Common Mistakes:

• Thinking array functions change PHP core speed
• Believing arrays can only hold numbers
• Confusing array functions with input validation

2. Which of the following is the correct syntax to count elements in an array $arr in PHP?

easy

A. length($arr);

B. size($arr);

C. count($arr);

D. countElements($arr);

Solution

1. Step 1: Recall PHP function for counting array elements

   The correct function to count elements in an array is count().

2. Step 2: Check each option

   Only count($arr); uses count($arr); which is valid PHP syntax. Others are not valid PHP functions.

3. Final Answer:

   count($arr); -> Option C

4. Quick Check:

   Counting array elements uses count() = B [OK]

Hint: Use count() to get array size quickly [OK]

Common Mistakes:

• Using length() which is not a PHP function
• Trying size() which doesn't exist in PHP
• Assuming countElements() is built-in

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

$numbers = [3, 1, 4, 1, 5];
sort($numbers);
print_r($numbers);

medium

A. [1, 1, 3, 4, 5]

B. Error: sort() is undefined

C. [3, 1, 4, 1, 5]

D. [5, 4, 3, 1, 1]

Solution

1. Step 1: Understand what sort() does

   The sort() function sorts the array in ascending order, changing the original array.

2. Step 2: Apply sort() to the array

   Sorting [3, 1, 4, 1, 5] ascending gives [1, 1, 3, 4, 5].

3. Final Answer:

   [1, 1, 3, 4, 5] -> Option A

4. Quick Check:

   sort() arranges numbers ascending = D [OK]

Hint: sort() arranges array ascending by default [OK]

Common Mistakes:

• Thinking sort() sorts descending by default
• Expecting original array unchanged
• Assuming sort() is not a built-in function

4. Identify the error in this PHP code snippet:

$fruits = ['apple', 'banana', 'cherry'];
$found = in_array('banana', $fruits);
if ($found = true) {
    echo 'Found banana!';
}

medium

A. Array syntax is incorrect

B. in_array() is not a valid PHP function

C. Echo statement is missing a semicolon

D. Using '=' instead of '==' in the if condition

Solution

1. Step 1: Check the if condition syntax

   The condition uses assignment '=' instead of comparison '==', so it always assigns true and evaluates as true.

2. Step 2: Correct the condition

   It should be if ($found == true) or simply if ($found) to check the boolean value.

3. Final Answer:

   Using '=' instead of '==' in the if condition -> Option D

4. Quick Check:

   Use '==' to compare, not '=' [OK]

Hint: Use '==' for comparison, '=' is assignment [OK]

Common Mistakes:

• Confusing '=' with '==' in conditions
• Thinking in_array() is invalid
• Missing semicolon after echo (actually present)

5. You have an array of user ages: $ages = [21, 17, 30, 15, 25];.
Using PHP array functions, which code snippet correctly filters out ages less than 18 and returns the filtered array?

hard

A. $adults = array_filter($ages, fn($age) => $age >= 18);

B. $adults = array_map(fn($age) => $age >= 18, $ages);

C. $adults = array_reduce($ages, fn($carry, $age) => $age >= 18 ? $age : $carry);

D. $adults = array_search(fn($age) => $age >= 18, $ages);

Solution

1. Step 1: Understand the goal

   We want to keep only ages 18 or older, so we need a function that filters elements based on a condition.

2. Step 2: Identify correct array function

   array_filter() keeps elements where the callback returns true. $adults = array_filter($ages, fn($age) => $age >= 18); uses it correctly with a function checking age >= 18.

3. Step 3: Check other options

   $adults = array_map(fn($age) => $age >= 18, $ages); uses array_map() which transforms elements but does not filter. $adults = array_reduce($ages, fn($carry, $age) => $age >= 18 ? $age : $carry); uses array_reduce() incorrectly for filtering. $adults = array_search(fn($age) => $age >= 18, $ages); uses array_search() wrongly with a callback.

4. Final Answer:

   $adults = array_filter($ages, fn($age) => $age >= 18); -> Option A

5. Quick Check:

   Use array_filter() to select elements by condition [OK]

Hint: Use array_filter() to keep elements matching condition [OK]

Common Mistakes:

• Using array_map() instead of array_filter() for filtering
• Misusing array_reduce() for filtering
• Trying to use array_search() with a callback