Fibonacci series in two ways: Recursive and for loop

fibonacci-series.php

<?php
/**
 * Fibonacci series as simple for loop
 */
function fibonacciLoop($n) {
    $series = [0, 1];
    if ($n == 0 || $n == 1) {
        return $n;
    }
    for ($i=2; $i<=$n; $i++) {
        $series[] = $series[$i - 2] + $series[$i - 1];
    }
    
    return $series[$n];
}
print fibonacciLoop(4); // 3

/**
 * Fibonacci series as recursive function
 */
function fibonacciRecursive($n) {
    if ($n == 0 || $n == 1) {
        return $n;
    }
    return fibonacciRecursive($n - 2) + fibonacciRecursive($n - 1);
}
print fibonacciRecursive(4); // 3