c# Döviz Hesaplama

namespace coklu_fonksiyon
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        double kur(string tip)
        {
            double kurdeger;
            switch (tip)
            {
                case "Dolar":
                    kurdeger=1.20;
                    break;  
                case "Euro":
                    kurdeger=1.70;
                    break;
                case "Sterlin":
                    kurdeger=2.70;
                    break;
                default:
                    kurdeger=1;
                    break;
            }
            return kurdeger;
         }
        double kurhesapla(double para, string kurcinsi)
        {
            return para * kur(kurcinsi);
        }
        private void button1_Click(object sender, EventArgs e)
        {
            int para = Convert.ToInt16(textBox1.Text);
            string doviz =comboBox1.Text;
            textBox2.Text=Convert.ToString(kurhesapla(double.Parse(textBox1.Text),doviz));
        }
    }
}