Optional Function Parameters in PHP

Function parameters can be made optional. To do this, parameters need to be given default values. Let's say for example we have the following function:

<?php
	function func($num) {
		echo $num ** 2;
	}
?>

Let's make it so that this parameter defaults to the value 0:

<?php
	function func($num = 0) {
		echo $num ** 2;
	}
?>

Let's test our function with a parameter:

<?php
	func(2); // outputs 4
?>

Let's test our function without a parameter:

<?php
	func(); // outputs 0
?>

Given the function:

<?php
	function func($num = 5) {
		echo $num * $num;
	}
?>

This function is called in the following way:

<?php
	func(2);
	func(3);
	func();
?>

Explain what the result of each function call will be.

Given the function:

<?php
	function func($num1 = 0, $num2 = 0) {
		echo $num1 + $num2;
	}
?>

This function is called in the following way:

<?php
	func(2, 3);
	func(3);
	func();
?>

Explain what the result of each function call will be.