DateTime Tarih = DateTime.Today.AddDays(-1);
string ay = Tarih.Month.ToString().PadLeft(2, '0');
string gun = Tarih.Day.ToString().PadLeft(2, '0');
string kur = string.Format("http://www.tcmb.gov.tr/kurlar/{0}{1}/{2}{1}{0}.xml", Tarih.Year, ay, gun);
var xmlDoc1 = new XmlDocument();
xmlDoc1.Load(kur);


string USDd = xmlDoc1.SelectSingleNode("Tarih_Date/Currency [@Kod='USD']/ForexBuying").InnerXml;
usddunku.Text = string.Format("{1}", tarih.ToShortDateString(), USDd);

string EURd = xmlDoc1.SelectSingleNode("Tarih_Date/Currency [@Kod='EUR']/ForexBuying").InnerXml;
eurodunku.Text = string.Format("{1}", tarih.ToShortDateString(), EURd);

string GBPd = xmlDoc1.SelectSingleNode("Tarih_Date/Currency [@Kod='GBP']/ForexBuying").InnerXml;
gbpdunku.Text = string.Format("{1}", tarih.ToShortDateString(), GBPd);

string CHFd = xmlDoc1.SelectSingleNode("Tarih_Date/Currency [@Kod='CHF']/ForexBuying").InnerXml;
chfdunku.Text = string.Format("{1}", tarih.ToShortDateString(), CHFd);