🔝 Top 20 PHP Interview Questions in Functions

1. What is a function in PHP?

A function is a block of code that performs a specific task and can be reused. It is defined using the function keyword.

2. How do you define a function in PHP?

function sayHello() {
    echo "Hello!";
}

3. What is the difference between built-in and user-defined functions in PHP?

• Built-in functions are provided by PHP (e.g., strlen(), array_merge()).
• User-defined functions are created by the developer using function.

Top 20 PHP Interview Questions in Functions

4. What are function arguments in PHP?

Arguments are values passed to a function when it is called:

function greet($name) {
    echo "Hello, $name!";
}

5. What is the default argument value in a function?

You can assign default values to parameters:

function greet($name = "Guest") {
    echo "Hello, $name!";
}

6. What is variable-length argument (variadic function) in PHP?

Using ... (splat operator):

function sum(...$numbers) {
    return array_sum($numbers);
}

7. What is a return statement in PHP functions?

It returns a value from the function:

function add($a, $b) {
    return $a + $b;
}

Top 20 PHP Interview Questions in Functions

8. What is recursion in PHP?

A function that calls itself:

function factorial($n) {
    if ($n <= 1) return 1;
    return $n * factorial($n - 1);
}

9. What is an anonymous function (closure)?

A function without a name, often used in callbacks:

$greet = function($name) {
    return "Hi $name";
};

10. What are arrow functions in PHP (from PHP 7.4+)?

Shorter syntax for anonymous functions:

$square = fn($n) => $n * $n;

Top 20 PHP Interview Questions in Functions

11. Can you pass a function as a parameter in PHP?

Yes, using callbacks:

function runCallback($callback) {
    return $callback("Test");
}

12. What is call_user_func() in PHP?

Used to call a function dynamically:

call_user_func('sayHello');

13. What is call_user_func_array()?

Used to call a function with arguments from an array:

function add($a, $b) {
    return $a + $b;
}
call_user_func_array('add', [3, 4]);

14. What is the difference between include() and require() inside a function?

Both include files, but require() will cause a fatal error if the file is missing; include() will only raise a warning.

Top 20 PHP Interview Questions in Functions

15. What is function_exists()?

Checks if a function has been defined:

if (function_exists('myFunction')) {
    myFunction();
}

16. What is the scope of a variable inside a function?

Variables declared inside a function are local to that function.

17. How do you access global variables inside a function?

Using the global keyword or $GLOBALS array:

function showName() {
    global $name;
    echo $name;
}

18. Can PHP functions return multiple values?

Yes, using arrays:

function getData() {
    return ["John", 25];
}

19. What is the use of declare(strict_types=1) in functions?

Enforces strict type-checking for function parameters and return values.

20. How to define a type hint for function parameters and return types?

function add(int $a, int $b): int {
    return $a + $b;
}

Top 20 PHP Interview Questions in Functions