Assign value to variable based on Database record count in ASP.Net

Hello guys , I have the next problem... I have a query and If the result of the query is greater than zero, the variablee re= "true" . but my code send me error 

 thnks!

I tried this :  

        public string Regla_4(string C_E)
        {

            string query = "SELECT COUNT (Empresas.CODIGO_EMPRESA) FROM Empresas WHERE Empresas.CODIGO_EMPRESA = @codigo";
            string R2 = "OK";

            string constr = ConfigurationManager.ConnectionStrings["Constring"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constr))
            {
                SqlCommand command = new SqlCommand(query, con);
                command.Parameters.Add("@codigo", SqlDbType.Int).Value = C_E;

                con.Open();
                command.ExecuteNonQuery();

                using (SqlDataReader sdr = command.ExecuteReader())
                {

                    if (sdr.HasRows)
                    {
                        while (sdr.Read())
                        {
                            if (sdr.GetInt16(0) > 0)
                            {
                                R2 = "TRUE";
                            }
                            else
                            {
                                R2 = "FALSE";
                            }
                        }
                    }
                } 
                return R2;
            }