Associative array creation in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of associative array creation with mixed keys

What is the output of the following PHP code?

PHP

<?php
$arr = ["a" => 1, 2 => "b", "3" => "c", 4 => "d"];
print_r($arr);
?>

A Array ( [0] => a [1] => 1 [2] => b [3] => c [4] => d )

B Array ( [a] => 1 [2] => b [3] => c [4] => d [0] => 0 )

C Array ( [a] => 1 [2] => b [3] => c [4] => d )

D Array ( [a] => 1 [2] => b [3] => c )

💡 Hint

Remember that numeric string keys are converted to integers in PHP arrays.

In PHP, string keys that are numeric strings like "3" are converted to integer keys. So the key "3" becomes 3. The array has keys 'a', 2, 3, and 4 with their respective values.

❓ Predict Output

intermediate

Count items in associative array created with array()

How many items does the following associative array contain?

PHP

<?php
$assoc = array('x' => 10, 'y' => 20, 'z' => 30);
echo count($assoc);
?>

A Error

B 0

C 1

D 3

💡 Hint

Count returns the number of key-value pairs in an array.

The array has three key-value pairs: 'x', 'y', and 'z'. So count returns 3.

🔧 Debug

advanced

Identify the error in associative array creation

What error does the following PHP code produce?

PHP

<?php
$arr = ["key1" => 100, "key2" 200, "key3" => 300];
print_r($arr);
?>

A Parse error: syntax error, unexpected '200' (missing =>)

B Notice: Undefined index 'key2'

C Warning: Array to string conversion

D No error, outputs the array

💡 Hint

Check the syntax for key-value pairs in arrays.

The key 'key2' is missing the => operator before its value 200, causing a syntax error.

🧠 Conceptual

advanced

Associative array key type behavior

Which statement about PHP associative array keys is TRUE?

A Null keys are converted to string 'null'

B Boolean true is converted to integer 1 as a key

C Arrays can be used as keys

D Float keys are stored as floats

💡 Hint

Think about how PHP converts different types to keys internally.

In PHP, boolean true is converted to integer 1 when used as an array key. Float keys are cast to integers. Null is cast to empty string. Arrays cannot be used as keys.

🚀 Application

expert

Create associative array from two lists

Given two arrays $keys = ['name', 'age', 'city'] and $values = ['Alice', 30, 'Paris'], which code correctly creates an associative array combining keys and values?

A $assoc = array_combine($keys, $values);

B $assoc = array_fill_keys($keys, $values);

C $assoc = array_map(fn($k, $v) => [$k => $v], $keys, $values);

D $assoc = array_merge($keys, $values);

💡 Hint

Look for a function that pairs keys and values into an associative array.

array_combine creates an associative array by using one array for keys and another for values. array_merge merges arrays sequentially. array_map returns an array of arrays, not a single associative array. array_fill_keys fills all keys with the same value.