public class CDB
        {
            private static SqlConnection conn;
            private SqlCommand cmd;

            public static void ConnectOpen(string DbName, string ServerName, string Login, string Pwd)
            {
                conn = new SqlConnection("database=" + DbName + ";server=" + ServerName + ";Uid=" + Login + ";Pwd=" + Pwd + ";");
                conn.Open();
            }

            public static void ConnectClose()
            {
                conn.Close();
            }

            public void ExcecCmd()
            {
                cmd = new SqlCommand();
                cmd.Connection = conn;
                cmd.CommandText = "...";
            }
        }

CDB.ConnectOpen("rokk_db", "Admin213", "sa", "gfhjkm");