euro-converter-example.php

<?php declare(strict_types=1);

class Converter 
{
    private const URL = 'http://www.cbr.ru/scripts/XML_daily.asp';
    private const CURRENCY_ID = 'R01239';

    /** @var DOMXPath|null */
    private $xpath = null;

    public function __construct()
    {
        \libxml_use_internal_errors(true);
        $doc = new DOMDocument();

        $content = file_get_contents(self::URL);
        $content = mb_convert_encoding($content, 'utf-8', 'windows-1251');

        $doc->loadXML($content);
        $this->xpath = new DOMXPath($doc);
    }

    public function convert(float $euro): float
    {
        $currency = $this->xpath->evaluate(sprintf('string(//Valute[@ID="%s"]/Value)', self::CURRENCY_ID));
        $currency = (float) str_replace(',', '.', $currency);

        return round($currency * $euro, 2);
    }
}

$c = new Converter();
var_dump($c->convert(10.1));