

<?php
$_POST['fibnum']=1;

if(isset($_POST['fibnum'])){


    $fibnum = $_POST['fibnum'];


    function fibRec($fibnum){

        if ($fibnum < 0){
        return ( "There are no Fibonacci numbers of negative values.");
        }
            elseif ($fibnum == 0){

                return ("0");
            }

                elseif ($fibnum == 1){

                    return ("1");
                }

                    else {

                        $sum = fibRec($fibnum-1)+fibRec($fibnum-2); 
                        return ($sum);
                    }

    }
        $fib = fibRec($fibnum); 
        echo $fib;          

}           
?>