Null coalescing operator in PHP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the null coalescing operator (??) do in PHP?

It returns the value of the left operand if it exists and is not null; otherwise, it returns the right operand.

intermediate

How is the null coalescing operator different from the ternary operator?

The null coalescing operator only checks if a value is set and not null, while the ternary operator evaluates a condition and returns one of two values based on that condition.

beginner

Example: What will this code output?<br>

$name = null;<br>echo $name ?? 'Guest';

It will output 'Guest' because $name is null, so the operator returns the right side value.

intermediate

Can the null coalescing operator be chained? Give an example.

Yes, it can be chained to check multiple variables. Example:<br>

$username = $_GET['user'] ?? $_POST['user'] ?? 'anonymous';

beginner

When was the null coalescing operator introduced in PHP?

It was introduced in PHP 7.0 to simplify checking for null or unset variables.

What will this PHP code output?<br>

$a = null;<br>$b = 'Hello';<br>echo $a ?? $b;

A null

B Hello

C Error

D Empty string

Since $a is null, the operator returns $b which is 'Hello'.

Which PHP version introduced the null coalescing operator (??)?

A PHP 5.6

B PHP 7.4

C PHP 7.0

D PHP 8.0

The null coalescing operator was introduced in PHP 7.0.

What does the null coalescing operator check for?

A If a variable is true

B If a variable is empty string

C If a variable is false

D If a variable is set and not null

It checks if the variable exists and is not null.

Which of these is a valid use of the null coalescing operator?

A $value = $x ?? 'default';

B $value = $x ? 'default';

C $value = $x ?: 'default';

D $value = $x || 'default';

The syntax $x ?? 'default' is correct for null coalescing.

Can the null coalescing operator be used to check multiple variables in one expression?

A Yes, by chaining multiple ?? operators

B No, only one variable at a time

C Only with arrays

D Only inside functions

You can chain ?? operators to check several variables in order.

Explain how the null coalescing operator works in PHP and give a simple example.

Think about checking if a variable exists or has a value, then providing a fallback.

Describe a situation where chaining the null coalescing operator is useful.

Imagine getting user input from different sources with fallback defaults.