Nullable types in functions in PHP - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of function with nullable int parameter

What is the output of this PHP code when calling describeAge(null);?

PHP

<?php
function describeAge(?int $age): string {
    if ($age === null) {
        return "Age is unknown.";
    }
    return "Age is $age.";
}
echo describeAge(null);

A Age is unknown.

B Age is 0.

C Age is null.

D TypeError

💡 Hint

Remember that the question mark before int means the parameter can be null.

The function accepts an int or null. When null is passed, it returns 'Age is unknown.' because of the explicit check.

❓ Predict Output

intermediate

Return type with nullable string

What will this PHP code output when calling getName(null);?

PHP

<?php
function getName(?string $name): ?string {
    if ($name === null) {
        return null;
    }
    return strtoupper($name);
}
var_dump(getName(null));

A TypeError

B "NULL"

C string(0) ""

D NULL

💡 Hint

The function returns null explicitly if input is null.

The function returns null when input is null, so var_dump outputs NULL without quotes.

❓ Predict Output

advanced

Nullable type with default value

What is the output of this PHP code when calling greet();?

PHP

<?php
function greet(?string $name = null): string {
    return $name ? "Hello, $name!" : "Hello, guest!";
}
echo greet();

A Hello, guest!

B Hello, !

C Hello, null!

D TypeError

💡 Hint

The default value is null and the function checks if $name is truthy.

Since no argument is passed, $name is null, which is falsy, so it returns 'Hello, guest!'.

❓ Predict Output

advanced

Nullable type with strict type enforcement

What happens when this PHP code runs?

PHP

<?php
declare(strict_types=1);
function multiply(?int $a, int $b): int {
    return ($a ?? 1) * $b;
}
echo multiply(null, 5);

A TypeError

B 5

C 0

D null

💡 Hint

The null coalescing operator replaces null with 1 before multiplication.

Since $a is null, ($a ?? 1) becomes 1, so 1 * 5 = 5 is returned and printed.

❓ Predict Output

expert

Nullable type with union and default

What is the output of this PHP code?

PHP

<?php
function format(?string|int $value = null): string {
    return match (true) {
        is_int($value) => "Number: $value",
        is_string($value) => "Text: $value",
        default => "No value",
    };
}
echo format();

A Number: 0

B TypeError

C No value

D Text:

💡 Hint

The default parameter is null, which matches the default case in match.

Since $value is null, none of the first two conditions match, so 'No value' is returned.