这样写for循环错在哪？为什么页面没反应？

Question

int id=(int)Session["userid"];

           string str = ConfigurationManager.ConnectionStrings["shuju"].ConnectionString;
           SqlConnection conn = new SqlConnection(str);
           for (int i = id; i < i + 4; i++)
           {
           string sql = " select * from [user] where grade ="+i+ "";
           SqlCommand cmd = new SqlCommand(sql, conn);
           SqlDataAdapter da = new SqlDataAdapter();
           da.SelectCommand = cmd;
           DataTable dt = new DataTable();
           da.Fill(dt);
           DataList1.DataSource = dt;
           DataList1.DataBind();
       }

Answer 1

for (int i = id; i < i + 4; i++)
死循环了，i < i+4永远成立

 for (int i = id,j=i+4; i<j; i++)