Fibonacci Series in PHP: Program with Examples

Introduction

In PHP, generating the Fibonacci series is a common beginner and interview-level question. It helps developers understand loops, recursion, and number patterns.

In this article, you will learn what the Fibonacci series is and how to implement it in PHP using different approaches.

What is the Fibonacci Series?

The Fibonacci series is a sequence of numbers where each number is the sum of the two preceding numbers.

The series starts with:

0, 1, 1, 2, 3, 5, 8, 13, 21…

Formula:

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

Syntax (General Logic)

To generate Fibonacci series:

1. Initialize first two numbers (0 and 1)
2. Add them to get next number
3. Continue the process

Examples

Example 1: Fibonacci Using for Loop

<?php
$n = 10;
$a = 0;
$b = 1;
echo $a . " " . $b . " ";
for ($i = 2; $i < $n; $i++) {
   $c = $a + $b;
   echo $c . " ";
   $a = $b;
   $b = $c;
}
?>

Output:

Example 2: Fibonacci Using while Loop

<?php
$n = 10;
$a = 0;
$b = 1;
$count = 2;
echo $a . " " . $b . " ";
while ($count < $n) {
   $c = $a + $b;
   echo $c . " ";
   $a = $b;
   $b = $c;
   $count++;
}
?>

Example 3: Fibonacci Using Recursion

<?php
function fibonacci($n) {
   if ($n == 0) return 0;
   if ($n == 1) return 1;
   return fibonacci($n - 1) + fibonacci($n - 2);
}
for ($i = 0; $i < 10; $i++) {
   echo fibonacci($i) . " ";
}
?>

Example 4: Fibonacci with User Input

<?php
$n = 5;
$a = 0;
$b = 1;
for ($i = 0; $i < $n; $i++) {
   echo $a . " ";
   $temp = $a + $b;
   $a = $b;
   $b = $temp;
}
?>

Example 5: Store Fibonacci in Array

<?php
$n = 10;
$fib = [];
$fib[0] = 0;
$fib[1] = 1;
for ($i = 2; $i < $n; $i++) {
   $fib[$i] = $fib[$i - 1] + $fib[$i - 2];
}
print_r($fib);
?>

Real-Life Example

Scenario 1 : Population Growth Model

Fibonacci series is used to model population growth patterns.

Scenario 2: Financial Market Analysis

Traders use Fibonacci levels to predict stock price movements.

Scenario 3: UI/UX Design

Fibonacci ratios are used in layout design for better visual balance.

Common Mistakes

1. Wrong Initialization

$a = 1; $b = 1;

👉 Correct is 0 and 1.

2. Infinite Loop

Incorrect loop condition may cause infinite execution.

3. Wrong Formula

$c = $a * $b;

Should be an addition.

4. Recursion Without Base Case

Leads to infinite recursion.

5. Large Input in Recursion

Recursive approach is slow for large values.

Conclusion

The Fibonacci series in PHP is an essential concept for understanding sequences, loops, and recursion. It is widely used in programming, mathematics, and real-world applications.

By mastering Fibonacci logic, you can:

• Improve problem-solving skills
• Understand recursion deeply
• Write efficient algorithms