PHP Program for Nth Fibonacci Number

The Fibonacci sequence is a series of numbers where each number is the sum of the two preceding ones, usually starting with 0 and 1. In this article, we will write a PHP program to find the Nth Fibonacci number.

Iterative Method

First, we define a function that takes an integer $n as a parameter. Inside the function, we initialize two variables, $f1 and $f2 with 0 and 1 respectively. These represent the first two numbers in the Fibonacci sequence.

Then we use a for loop to calculate the Fibonacci sequence up to the Nth number. The loop starts from 2 because the first two numbers are already initialized. In each iteration, we calculate the next Fibonacci number and update the values of $f1 and $f2 accordingly. The function returns the value of the Nth Fibonacci number, which is stored in the variable $f2.

PHP

<?php

function fibNumber($n) {
    $f1 = 0;
    $f2 = 1;

    for ($i = 2; $i <= $n; $i++) {
        $next = $f1 + $f2;
        $f1 = $f2;
        $f2 = $next;
    }

    return $f2;
}

// Driver Code
$n = 10;

echo "The {$n}th Fibonacci number is: "
    . fibNumber($n);
?>

Output

The 10th Fibonacci number is: 55

Recursive Method

A recursive solution involves defining a function that calls itself to solve subproblems. First, we call a function with number $n i.e. fibNumber($n), and then check if number is less then or equal to 1, then it returns number, otherwise it returns fibNumber($n – 1) + fibNumber($n – 2).

PHP

<?php
function fibNumber($n) {
    if ($n <= 1) {
        return $n;
    }

    return fibNumber($n - 1) + fibNumber($n - 2);
}

// Driver Code
$n = 10;

echo "The {$n}th Fibonacci number is: "
    . fibNumber($n);
?>

Output

The 10th Fibonacci number is: 55