string USDy = xmlDoc1.SelectSingleNode("Tarih_Date/Currency [@Kod='USD']/ForexBuying").InnerXml;
string EURy = xmlDoc1.SelectSingleNode("Tarih_Date/Currency [@Kod='EUR']/ForexBuying").InnerXml;
string GBPy = xmlDoc1.SelectSingleNode("Tarih_Date/Currency [@Kod='GBP']/ForexBuying").InnerXml;
string CHFy = xmlDoc1.SelectSingleNode("Tarih_Date/Currency [@Kod='CHF']/ForexBuying").InnerXml;

int usdyuzdeli = Convert.ToInt32(Convert.ToDouble(USDy) * 5 / 100);
int euroyuzdeli = Convert.ToInt32(Convert.ToDouble(EURy) * 5 / 100);
int gbpyuzdeli = Convert.ToInt32(Convert.ToDouble(GBPy) * 5 / 100);
int chfyuzdeli = Convert.ToInt32(Convert.ToDouble(CHFy) * 5 / 100);

double usdyuz5 = Convert.ToDouble(USDy) - Convert.ToDouble(usdyuzdeli);
double euryuz5 = Convert.ToDouble(EURy) - Convert.ToDouble(usdyuzdeli);
double gbpyuz5 = Convert.ToDouble(GBPy) - Convert.ToDouble(usdyuzdeli);
double chfyuz5 = Convert.ToDouble(CHFy) - Convert.ToDouble(usdyuzdeli);

usd5.Text = string.Format("{0}", Convert.ToDouble(usdyuz5));
usd5.Text = string.Format("{0}", Convert.ToDouble(euryuz5));
usd5.Text = string.Format("{0}", Convert.ToDouble(gbpyuz5));
usd5.Text = string.Format("{0}", Convert.ToDouble(chfyuz5));