public class Currency
        {
            public string Tarih { get; set; }
            public string Kod { get; set; }
            public string CurrencyCode { get; set; }
            public string CrossOrder { get; set; }
            public string Unit { get; set; }
            public string Isim { get; set; }
            public string CurrencyName { get; set; }
            public double ForexBuying { get; set; }
            public double ForexSelling { get; set; }
            public double BanknoteBuying { get; set; }
            public double BanknoteSelling { get; set; }
            public double CrossRateUSD { get; set; }
            public double CrossRateOther { get; set; }
        }
        public static List<Currency> GetCurrencies(DateTime Tarih)
        {
            if (Tarih.DayOfWeek == DayOfWeek.Saturday || Tarih.DayOfWeek == DayOfWeek.Sunday)
                return null;
            System.Threading.Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("en-US");
            List<Currency> currenciesL = new List<Currency>();
            string yearmonth = Tarih.ToString("yyyyMM");
            string monthyear = Tarih.ToString("MMyyyy");
            string day = Tarih.ToString("dd");
            string url = "";
            if (Tarih == DateTime.Now.Date)
                url = "https://www.tcmb.gov.tr/kurlar/today.xml"; 
            else url = "https://www.tcmb.gov.tr/kurlar/" + yearmonth + "/" + day + monthyear + ".xml";
            System.Net.WebRequest request = System.Net.WebRequest.Create(url);
            System.Net.WebResponse response = request.GetResponse();
            System.IO.StreamReader reader = new System.IO.StreamReader(response.GetResponseStream());
            string xml = reader.ReadToEnd();
            reader.Close();
            response.Close();
            System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
            doc.LoadXml(xml);
            System.Xml.XmlNodeList nodes = doc.SelectNodes("Tarih_Date/Currency");
            foreach (System.Xml.XmlNode node in nodes)
            {
                Currency currency = new Currency();
                currency.Tarih = Tarih.ToString("dd.MM.yyyy");
                currency.Kod = node.Attributes["Kod"].Value;
                currency.CurrencyCode = node.Attributes["CurrencyCode"].Value;
                currency.CrossOrder = node.Attributes["CrossOrder"].Value;
                currency.Unit = node.SelectSingleNode("Unit").InnerText;
                currency.Isim = node.SelectSingleNode("Isim").InnerText;
                currency.CurrencyName = node.SelectSingleNode("CurrencyName").InnerText;
                try { currency.ForexBuying = Convert.ToDouble(node.SelectSingleNode("ForexBuying").InnerText); } catch { }
                try { currency.ForexSelling = Convert.ToDouble(node.SelectSingleNode("ForexSelling").InnerText); } catch { }
                try { currency.BanknoteBuying = Convert.ToDouble(node.SelectSingleNode("BanknoteBuying").InnerText); } catch { }
                try { currency.BanknoteSelling = Convert.ToDouble(node.SelectSingleNode("BanknoteSelling").InnerText); } catch { }
                try { currency.CrossRateUSD = Convert.ToDouble(node.SelectSingleNode("CrossRateUSD").InnerText); } catch { }
                try { currency.CrossRateOther = Convert.ToDouble(node.SelectSingleNode("CrossRateOther").InnerText); } catch { }
                currenciesL.Add(currency);
            }
            return currenciesL;
        }

//Form içinde örnek kullanım:
        private void sb_Currencies_Click(object sender, EventArgs e)
        {
            //if datetime is saturday or sunday 
            if (de_CurrencyDate.DateTime.DayOfWeek == DayOfWeek.Saturday || de_CurrencyDate.DateTime.DayOfWeek == DayOfWeek.Sunday)
            {
                MessageBox.Show("Hafta Sonu Para Birimleri Alınamaz", "HATA", MessageBoxButtons.OK, MessageBoxIcon.Error);
                return;
            }
            List<Methods.Currency> CURRENCIES = Methods.GetCurrencies(de_CurrencyDate.DateTime);
            te_Usd.Text = CURRENCIES.Where(x => x.CurrencyCode == "USD").FirstOrDefault().ForexSelling.ToString();
            te_Eur.Text = CURRENCIES.Where(x => x.CurrencyCode == "EUR").FirstOrDefault().ForexSelling.ToString();
            te_Gbp.Text = CURRENCIES.Where(x => x.CurrencyCode == "GBP").FirstOrDefault().ForexSelling.ToString();
            te_EurUsdParite.Text = CURRENCIES.Where(x => x.CurrencyCode == "EUR").FirstOrDefault().CrossRateOther.ToString();
        }