写了个程序，想把计算得到的S、i值输入到数据库内，可是运行后的结果是在数据库内显示的是s、i的字母，而不是计算得到的s、i的数值。请帮忙解惑。谢谢！
SqlConnection cod = new SqlConnection("data source=localhost;uid=sa;pwd=;database=nihao");
                        cod.Open();

            double s = 0;
            string a, b;
            double c, d;
            double i = 2;
            
            for (int i = 0; i < 10; i++)
            {
                s = s + i;
                a = s.ToString();
                b = i.ToString();
                c = s;
                d = i;
                               SqlCommand cnd = new SqlCommand("insert into nihao(hao,xie)values('s','i')", cod);            
                                cnd.ExecuteNonQuery();
            }      
                       cod.Close();