Exchange-rate by yahoo

step 1
using System.Net;
using System.Text;
using System.Text.RegularExpressions;

step2
create class ConvertCurrency
public static decimal ConvertCurrency(decimal amount, string from, string to)
        {
            try
            {
                WebClient web = new WebClient();
                const string urlPattern = "http://finance.yahoo.com/d/quotes.csv?s={0}{1}=X&f=l1";
                string url = String.Format(urlPattern, from, to);
                string response = new WebClient().DownloadString(url);
                decimal exchangeRate = decimal.Parse(response, System.Globalization.CultureInfo.InvariantCulture);
                return exchangeRate;
            }
            catch (Exception ex)
            {
                return 0;
            }
        }

step 3
core function
decimal apiRate = 0;
            apiRate =Class1.ConvertCurrency(1, "USD", "THB");