Array search functions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code using array_search?

Consider the following PHP code snippet. What will it output?

PHP

<?php
$array = ['apple', 'banana', 'cherry'];
$pos = array_search('banana', $array);
echo $pos;
?>

A 0

B 1

C 2

D false

💡 Hint

Remember that array_search returns the key of the found element.

The array has 'banana' at index 1, so array_search returns 1.

❓ Predict Output

intermediate

What does array_search return when the element is not found?

What will this PHP code output?

PHP

<?php
$array = ['red', 'green', 'blue'];
$result = array_search('yellow', $array);
var_dump($result);
?>

A bool(false)

B int(0)

C NULL

D string('')

💡 Hint

Check what array_search returns if the value is not found.

array_search returns false if the searched value is not found in the array.

🔧 Debug

advanced

Why does this array_search code produce unexpected output?

Look at this PHP code. It tries to find the key of the value 0 in the array. What is the output and why?

PHP

<?php
$array = [0 => 'zero', 1 => 'one', 2 => 'two'];
$key = array_search(0, $array);
echo $key === false ? 'Not found' : $key;
?>

A 0

B 2

C Not found

D 1

💡 Hint

Check the types of values in the array and what is searched.

The array contains strings, but the search is for integer 0, which is not found, so array_search returns false.

❓ Predict Output

advanced

What is the output when using strict comparison in array_search?

What will this PHP code output?

PHP

<?php
$array = ['1', '2', '3'];
$key = array_search(1, $array, true);
echo $key === false ? 'Not found' : $key;
?>

A Not found

B 1

C 0

D 2

💡 Hint

Strict comparison checks both value and type.

With strict=true, integer 1 is not equal to string '1', so array_search returns false.

🧠 Conceptual

expert

How many elements are in the array after this code?

What is the number of elements in the array after this PHP code runs?

PHP

<?php
$array = ['a' => 1, 'b' => 2, 'c' => 3];
$key = array_search(2, $array);
if ($key !== false) {
    unset($array[$key]);
}
echo count($array);
?>

A 0

B 1

C 3

D 2

💡 Hint

Removing one element reduces the count by one.

array_search finds key 'b', unset removes it, so array has 2 elements left.

Practice

1. Which PHP function returns the key of a value in an array if found, or false if not found?

easy

A. in_array

B. array_search

C. array_key_exists

D. array_keys

Solution

1. Step 1: Understand function purpose

   array_search looks for a value and returns its key if found.

2. Step 2: Compare with other functions

   in_array returns true/false, not key; array_key_exists checks keys; array_keys returns all keys.

3. Final Answer:

   array_search -> Option B

4. Quick Check:

   Key returned by array_search = array_search [OK]

Hint: array_search returns key, in_array returns true/false [OK]

Common Mistakes:

• Confusing array_search with in_array
• Thinking array_key_exists returns value
• Assuming array_keys searches values

2. Which of the following is the correct syntax to check if the value 5 exists in array $arr using in_array?

easy

A. in_array(5, $arr);

B. in_array($arr, 5);

C. in_array($arr => 5);

D. in_array(5 => $arr);

Solution

1. Step 1: Recall in_array syntax

   The correct syntax is in_array(value, array).

2. Step 2: Match syntax with options

   in_array(5, $arr); matches in_array(5, $arr); which is correct.

3. Final Answer:

   in_array(5, $arr); -> Option A

4. Quick Check:

   in_array(value, array) = in_array(5, $arr) [OK]

Hint: Remember in_array(value, array) order [OK]

Common Mistakes:

• Swapping parameters order
• Using arrow syntax instead of comma
• Passing array as first argument

3. What is the output of the following PHP code?

$arr = ['apple', 'banana', 'cherry'];
$key = array_search('banana', $arr);
echo $key;

medium

A. 0

B. banana

C. false

D. 1

Solution

1. Step 1: Understand array_search behavior

   It returns the key of the searched value if found.

2. Step 2: Check array keys and searched value

   Array keys are 0=>'apple', 1=>'banana', 2=>'cherry'. Searching 'banana' returns key 1.

3. Final Answer:

   1 -> Option D

4. Quick Check:

   array_search('banana', $arr) = 1 [OK]

Hint: array_search returns index/key of found value [OK]

Common Mistakes:

• Expecting value instead of key
• Confusing false with 0
• Assuming it returns boolean

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

$arr = ['x' => 10, 'y' => 20];
if (array_search(30, $arr)) {
    echo 'Found';
} else {
    echo 'Not Found';
}

medium

A. array_search returns false but condition treats 0 as false

B. array_search returns key but 30 is not in array, so condition fails correctly

C. array_search should be replaced with in_array for this check

D. No error, code works as expected

Solution

1. Step 1: Analyze array_search return and condition

   array_search returns key or false. If key is 0, condition fails because 0 is falsey.

2. Step 2: Check searched value presence

   30 is not in array, so array_search returns false, condition is false, prints 'Not Found'. But if value was at key 0, condition would fail incorrectly.

3. Step 3: Suggest correct function for boolean check

   Use in_array which returns true/false directly for presence check.

4. Final Answer:

   array_search should be replaced with in_array for this check -> Option C

5. Quick Check:

   Use in_array for boolean presence check [OK]

Hint: Use in_array for true/false presence checks [OK]

Common Mistakes:

• Using array_search in if without strict check
• Ignoring 0 key treated as false
• Not using === to check false

5. Given the array $data = ['a' => 0, 'b' => false, 'c' => null, 'd' => '0'];, which function call correctly checks if the value 0 exists in the array considering type?

hard

A. in_array(0, $data, true);

B. array_search(0, $data);

C. in_array(0, $data);

D. array_search('0', $data, true);

Solution

1. Step 1: Understand strict checking

   Using third parameter true enforces type checking in in_array and array_search.

2. Step 2: Analyze array values and types

   Values are 0 (int), false (bool), null, and '0' (string). Only strict check distinguishes 0 (int) from others.

3. Step 3: Choose correct function and parameters

   in_array(0, $data, true) returns true only if exact int 0 found. array_search without strict may confuse types.

4. Final Answer:

   in_array(0, $data, true); -> Option A

5. Quick Check:

   Use in_array with strict=true for exact type match [OK]

Hint: Use in_array with strict=true to check exact value and type [OK]

Common Mistakes:

• Ignoring strict parameter causing false positives
• Using array_search without strict for type-sensitive check
• Confusing '0' string with 0 integer