Fibonacci series of numbers in PHP by using for loop and recursive function

In Fibonacci series of numbers, each number is the sum of the two preceding ones.

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377

Fn = F(n-1) + F(n-2)

Generating Fibonacci series in PHP where any number is sum of previous two numbers

Generating Fibonacci series using for loop

We will use for loop to generate the series.

$n1=1; // first number 
$n2=0; // second number
for($i=0;$i<=15;$i++){
echo " $n2,";
$temp=$n1+$n2; // temporary variable  
$n1=$n2;   // $n2 value shifted to $n1 
$n2=$temp; // temporary value ( sum ) is shifted. 	
}

Output

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610,

Using recursive function

function fibo($n){
if($n<=1){
return $n;}
else{
	return (fibo($n-1)+fibo($n-2));
}	
}

for ($i=0;$i<15;$i++){
echo fibo($i).", ";
}

Output

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377,

Question

Write a PHP function, generateFibonacci(), that accepts an argument to represent a number (n) and displays the nth number in the Fibonacci series . The series is 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144… For example, invoking the function using the statement generateFibonacci(3)should display 1 as the output, as 5 is the 6th number in the series

<?php
function generateFibonacci($n) {
    if ($n < 1) {
        echo "Invalid input. Please enter a positive integer.";
        return;
    }

    // Handle the first two numbers
    if ($n == 1) {
        echo "0";
        return;
    } elseif ($n == 2) {
        echo "1";
        return;
    }

    // Generate Fibonacci for n >= 3
    $a = 0;
    $b = 1;
    for ($i = 3; $i <= $n; $i++) {
        $temp = $a + $b;
        $a = $b;
        $b = $temp;
    }

    echo "" . $b . "";
}

// Example usage
//generateFibonacci(7); // Output: 8
//generateFibonacci(3); // Output: 1
generateFibonacci(1); // Output: 0
?>

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