Null type and its meaning in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this PHP code with null?

Look at this PHP code. What will it print?

PHP

<?php
$value = null;
if (is_null($value)) {
    echo 'Yes';
} else {
    echo 'No';
}
?>

A No

B Yes

C null

D Error

💡 Hint

Check what is_null() does when the variable is null.

The function is_null() returns true if the variable is null. So it prints 'Yes'.

❓ Predict Output

intermediate

What is the output when comparing null with empty string?

What will this PHP code print?

PHP

<?php
var_dump(null == '');
var_dump(null === '');
?>

A bool(false) bool(false)

B bool(true) bool(true)

C bool(true) bool(false)

D bool(false) bool(true)

💡 Hint

Remember that == checks value equality with type juggling, === checks type and value.

Using ==, null and empty string are not considered equal (false). Using ===, types differ so false.

🔧 Debug

advanced

Why does this code cause a warning with null?

Find the reason for the warning in this PHP code:

PHP

<?php
$value = null;
echo strlen($value);
?>

A Warning because strlen() expects a string, null is not a string

B Warning because null cannot be echoed directly

C No warning, it prints 0

D Fatal error because null is undefined

💡 Hint

Check what type strlen() expects as input.

strlen() expects a string. Passing null causes a warning because null is not a string.

🧠 Conceptual

advanced

What does the null coalescing operator do in PHP?

Choose the best description of the null coalescing operator ?? in PHP.

A Assigns null to the left variable if the right is null

B Returns true if both values are null

C Returns the left value if it is not null, otherwise returns the right value

D Checks if both values are equal and not null

💡 Hint

Think about how to provide a default value when a variable might be null.

The operator ?? returns the left operand if it is not null; otherwise, it returns the right operand.

❓ Predict Output

expert

What is the output of this PHP code mixing null and arrays?

What will this PHP code print?

PHP

<?php
$array = ['a' => null, 'b' => 0, 'c' => false];
$count = 0;
foreach ($array as $key => $value) {
    if ($value == null) {
        $count++;
    }
}
echo $count;
?>

A 1

B 0

C 3

D 2

💡 Hint

Remember that == null is true for null and false, but not for 0 in PHP.

In PHP, == null is true for null and false, but not for 0. So keys 'a' and 'c' match, count is 2.