<?php
if(!function_exists('kdv'))
{
    function kdv($rakam,$oran=18,$islem='-')
    {
        $oranhesap = ($oran/100);
        switch($islem)
        {
            case '-';
                $kdvrakam = (1+$oranhesap);
                $rakam = @number_format($rakam/$kdvrakam, 2, '.', ',');
            break;
            case '+';
                $kdvrakam = (100*($oranhesap));
                $rakam = @number_format($rakam+$kdvrakam, 2, '.', ',');
            break;
            case '-+';
                $kdvrakam = (1+$oranhesap);
                $rakam = @number_format($rakam-$rakam/$kdvrakam, 2, '.', ',');
            break;
            case '+-';
                $kdvrakam = (100*($oranhesap));
                $rakam = @number_format($kdvrakam, 2, '.', ',');
            break;
        }
        return @number_format($rakam, 2, '.', ',');
    }
}
/* fiyattan kdv düser, son fiyati doner */

echo kdv(118,18,'-'); // 1. parametre rakam, 2. parametre kdv oran , 3. parametre islem

echo '<hr>'; /* cizgi kodu onemsiz */



/* fiyata kdv ekler */

echo kdv(100,18,'+');

echo '<hr>'; /* cizgi kodu onemsiz */


/* cikacak kdvsini hesaplar */

echo kdv(118,18,'-+');

echo '<hr>'; /* cizgi kodu onemsiz */


/* eklenecek kdv hesapla */

echo kdv(100,18,'+-');

echo '<hr>'; /* cizgi kodu onemsiz */

?>