Recursion with a Parameter in PHP

Let's use recursion to sequentially output the elements of an array. Let the array initially be passed to the function parameter:

<?php
	func([1, 2, 3]);
?>

First, let's output all elements of the array one by one using the function array_shift without recursion:

<?php
	function func($arr) {
		var_dump(array_shift($arr)); // will output 1
		var_dump($arr); // will output [2, 3] - the array has shrunk
		
		var_dump(array_shift($arr)); // will output 2
		var_dump($arr); // will output [3] - the array has shrunk
		
		var_dump(array_shift($arr)); // will output 3
		var_dump($arr); // will output [] - the array is empty
	}
	
	func([1, 2, 3]);
?>

As you can see, the function array_shift extracts and returns the first element of the array, while the array itself is reduced by this element.

Now let's use recursion:

<?php
	function func($arr) {
		var_dump(array_shift($arr));
		var_dump($arr);
		
		if (count($arr) !== 0) {
			func($arr);
		}
	}
	
	func([1, 2, 3]);
?>

Of course, it is actually easiest to iterate over array elements with a loop. The examples given simply demonstrate the operation of recursion with simple (non-real-world) examples. More useful examples of recursion application are just more complex, we will analyze them a little later.

Given an array:

<?php
	$arr = ['a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5];
?>

Use recursion to output the elements of this array to the screen.