Null coalescing in conditions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of null coalescing with nested variables

What is the output of this PHP code snippet?

PHP

<?php
$a = null;
$b = 0;
$c = $a ?? $b ?? 5;
echo $c;
?>

A Error

B null

C 5

D 0

💡 Hint

Remember that null coalescing returns the first value that is not null.

The expression $a ?? $b ?? 5 returns the first non-null value. $a is null, so it checks $b which is 0 (not null), so it returns 0.

❓ Predict Output

intermediate

Null coalescing with undefined variable

What will this PHP code output?

PHP

<?php
// Note: error reporting is off for undefined variables
error_reporting(0);
$x = $undefinedVar ?? 'default';
echo $x;
?>

A Notice error

B null

C default

D Empty string

💡 Hint

Null coalescing operator handles undefined variables without error.

The null coalescing operator returns the right side if the left side is null or undefined. Since $undefinedVar is not set, it returns 'default'.

❓ Predict Output

advanced

Null coalescing with function return values

What is the output of this PHP code?

PHP

<?php
function getValue() {
    return null;
}
$result = getValue() ?? 'fallback';
echo $result;
?>

A fallback

B null

C Error: Cannot use null coalescing on function call

D Empty string

💡 Hint

Check what the function returns and how null coalescing handles it.

The function returns null, so the null coalescing operator returns the right side 'fallback'.

❓ Predict Output

advanced

Null coalescing with array keys

What will this PHP code output?

PHP

<?php
$arr = ['a' => null, 'b' => 2];
$value = $arr['a'] ?? $arr['b'] ?? 5;
echo $value;
?>

A 2

B null

C 5

D Error: Undefined index

💡 Hint

Null coalescing checks if the key exists and is not null.

The key 'a' exists but is null, so it moves to 'b' which is 2 (not null), so it returns 2.

❓ Predict Output

expert

Complex null coalescing with mixed types

What is the output of this PHP code?

PHP

<?php
$val1 = false;
$val2 = null;
$val3 = 0;
$result = $val1 ?? $val2 ?? $val3 ?? 'none';
echo gettype($result) . ':' . var_export($result, true);
?>

A integer:0

B boolean:false

C NULL:null

D string:'none'

💡 Hint

Null coalescing returns the first value that is not null, even if it is false or zero.

The first value $val1 is false but not null, so it returns false. The output shows type boolean and value false.