Learn how to implement the Fibonacci series in PHP. This tutorial explains how to code a PHP Fibonacci series with examples. Understanding this concept will improve your understanding of recursion and loops.

## What is a Fibonacci Series?

The Fibonacci series is a numerical sequence in which each number is the sum of the two numbers that come before it. Typically, the series begins with 0 and 1, following this pattern:

`0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, ...`

## Generating the Fibonacci Series in PHP

There are two main ways to generate the Fibonacci series in PHP: using a for loop and using recursion.

### Using a for Loop

The following code shows how to generate the Fibonacci series up to the 10th term using a for loop:

Example:

```
<?php
$first_num = 0;
$second_num = 1;
$n = 10; // Number of elements you want in the series
echo "Fibonacci Series: $first_num, $second_num";
for($i = 2; $i < $n; $i++) {
$next_num = $first_num + $second_num;
echo ", $next_num";
$first_num = $second_num;
$second_num = $next_num;
}
?>
```

Explanation:

In the above example, the variables `$first_num`

and `$second_num`

are initialized to hold the starting numbers of the Fibonacci sequence—0 and 1, respectively. The variable `$n`

sets the desired length of the series. Within the `for`

loop, `$next_num`

is calculated as the sum of `$first_num`

and `$second_num`

. These two variables are then updated in preparation for the next iteration, ensuring the series continues to generate accurately.

### Using Recursion

The following code shows how to generate the Fibonacci series up to the 10th term using recursion:

Example:

```
<?php
function fibonacci($n, $first_num = 0, $second_num = 1) {
if($n == 0) {
return;
}
echo $first_num . ", ";
$next_num = $first_num + $second_num;
fibonacci($n - 1, $second_num, $next_num);
}
$n = 10; // Number of elements you want in the series
echo "Fibonacci Series: ";
fibonacci($n);
?>
```

Explanation:

In the above example, the `fibonacci`

function primarily requires one argument, `$n`

, which specifies the length of the Fibonacci sequence to generate. The other two arguments, `$first_num`

and `$second_num`

, initialize and update the sequence. These are set by default to 0 and 1, the starting numbers of the Fibonacci sequence. The function uses recursion to call itself, decrementing `$n`

and updating the sequence numbers until `$n`

reaches zero, thereby completing the series.

#### Conclusion

Generating a Fibonacci series in PHP is a straightforward task. You can use either a for loop or recursion based on your project's needs. Both methods explained in this tutorial are efficient and help you understand the core concepts of programming and PHP.