基于php函数返回HTML PHP填充输入字段

Im trying to fill an input field, based on a php function return result, this is my code, i don't find a way to call the php function from html, im just new to PHP

This is my function

function get_cc_type($cardNumber)
{
$cardNumber = preg_replace('/\D/', '', $cardNumber);

$len = strlen($cardNumber);
if ($len < 15 || $len > 16) {
    throw new Exception("Tarjeta Invalida: verifique, e intente nuevamente.");
}
else {
    switch($cardNumber) {
        case(preg_match ('/^7(?:453|5)/', $cardNumber) >= 1):
            return 'KW Member';
        case(preg_match ('/^3(?:567|5)/', $cardNumber) >= 1):
            return 'VIP';
        default:
            throw new Exception("No es posible determinar el tipo de Tarjeta.");
            break;
    }
    }
}

<input type="text" name="card" required id="card" class="form-control input-lg" placeholder="Numero de Tarjeta" value="<?php if(isset($error)){ echo $_POST['card']; } ?>" tabindex="5" >
                <input type="button" onclick="document.write('<?php 'get_cc_type($card)' ?>');" value="Validar">

and this is the field i want to fill

<input type="text" name="cardtype" id="cardtype" class="form-control input-lg"     value="<?php $cardres; if(isset($error)){ echo $_POST['cardtype']; } ?>" tabindex="8">

i have just started today with php.

you can't use php code inside the html tag directly.

try using ajax. for example using jquery ajax

that's a simple way to use ajax