c# 向服务器post数据的时候 如何把参数和cookie一起发送

                System.Net.HttpWebRequest request;
                    request = (System.Net.HttpWebRequest)WebRequest.Create("http:www.xxxx.com");
                request.Method = "POST";
                request.ContentType = "application/x-www-form-urlencoded; charset=utf-8";
                string paraUrlCoded = System.Web.HttpUtility.UrlEncode(textBox4.Text);
                paraUrlCoded += "=" + System.Web.HttpUtility.UrlEncode(textBox3.Text);
                byte[] payload;
                payload = System.Text.Encoding.UTF8.GetBytes(paraUrlCoded);
                request.ContentLength = payload.Length;
                Stream writer = null;
                    writer = request.GetRequestStream();
                //将请求参数写入流
                writer.Write(payload, 0, payload.Length);
                // 关闭请求流
                writer.Close();
                System.Net.HttpWebResponse response = null;
                // 获得响应流
                    response = (System.Net.HttpWebResponse)request.GetResponse();
                System.IO.Stream s;
                s = response.GetResponseStream();
                StreamReader reader = new StreamReader(s);
                string strValue = reader.ReadToEnd();   //如果返回数据比较大，可以选择循环读取
                reader.Close();

如何发送cookie呢？
下面是火狐浏览器存储的cookie
PHPSESSID:"bjcjcq1q630hkmpjj5a65otev2"
_csrf:"91e0c51dd25fe28d57dcdb673c2b48a48ae843a820390ab8d8cc3f62ab9982b1a:2:{i:0;s:5:"_csrf";i:1;s:32:"TMuJAI2U_7A0qTdkNOKpTroujAdlL4s9";}"

用cookiecontainer，你是要采集需要身份验证的吧。。。demo
C#使用HttpWebRequest提交ASP.NET表单并保持Session和Cookie

HttpRequest r;
r.Cookies.Add(new HttpCookie(name, value));

根据http协议，cookie是放在请求头上，postdata放在正文里，你用fiddler抓包看下就知道了。