how to get the string value in class

string str=Combobox1.SelectedIndex.ToString();

class FTClientCode
       {

           public static string curMsg = "Idle";
           public static void SendFile(string fileName)
           {
               try
               {


                   IPAddress[] ipAddress = Dns.GetHostAddresses(str);
                   IPEndPoint ipEnd = new IPEndPoint(ipAddress[0], 5656);
                   Socket clientSock = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.IP);


                   string filePath = "";

                   fileName = fileName.Replace("\\", "/");
                   while (fileName.IndexOf("/") > -1)
                   {
                       filePath += fileName.Substring(0, fileName.IndexOf("/") + 1);
                       fileName = fileName.Substring(fileName.IndexOf("/") + 1);
                   }


                   byte[] fileNameByte = Encoding.ASCII.GetBytes(fileName);
                   if (fileNameByte.Length > 850 * 1024)
                   {
                       curMsg = "File size is more than 850kb, please try with small file.";
                       return;
                   }

                   curMsg = "Buffering ...";
                   byte[] fileData = File.ReadAllBytes(filePath + fileName);
                   byte[] clientData = new byte[4 + fileNameByte.Length + fileData.Length];
                   byte[] fileNameLen = BitConverter.GetBytes(fileNameByte.Length);

                   fileNameLen.CopyTo(clientData, 0);
                   fileNameByte.CopyTo(clientData, 4);
                   fileData.CopyTo(clientData, 4 + fileNameByte.Length);

                   curMsg = "Connection to server ...";
                   clientSock.Connect(ipEnd);

                   curMsg = "File sending...";
                   clientSock.Send(clientData);

                   curMsg = "Disconnecting...";
                   clientSock.Close();
                   curMsg = "File transferred.";

               }
               catch (Exception ex)
               {
                   if (ex.Message == "No connection could be made because the target machine actively refused it")
                       curMsg = "File Sending fail. Because server not running.";
                   else
                       curMsg = "File Sending fail." + ex.Message;
               }

           }
       }