using System;
using
using System.Data;
using System.Configuration;
using System.Drawing;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Data.SqlClient;

public partial class _select : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection("server=.; database=select;uid=sa;pwd=;");
        con.Open;
        SqlCommand cmd = new SqlCommand("select * from provence", con);
        SqlDataReader sdr = cmd.ExecuteReader();
        this.ddlPro.DataSource = sdr;
        this.ddlPro.DataTextField = "ProName";
        this.ddlPro.DataValueField = "ProID";
        this.ddlPro.DataBind();
        sdr.Close();
      
    //city的绑定
        SqlCommand citycmd = new SqlCommand("select * from City where ProID=" + this.ddlPro.SelectedValue, con);
        SqlDataReader sdrcity = citycmd.ExecuteReader();
        this.ddlCity.DataSource = sdrcity;
        this.ddlCity.DataTextField = "CityName";
        this.ddlCity.DataValueField = "CityID";
        this.ddlCity.DataBind();
        sdrcity.Close();
        con.Close();

    }
}


在con.Open;出现　CS0201: 只有 assignment、call、increment、decrement 和 new 对象表达式可用作语句
这是怎么回事？怎样才能解决？