C#中判断服务器图片是否存在

     public int num = 0;       /// <summary>
      /// 判断服务器路径中的图片文件是否存在存在则累加统计
      /// </summary>
    private int GetAcount(string name)
    {
        for (int i = 1; i < i + 1; i++)
        {
            string url = "http://IP/Image/" + name + "/" + name + i + ".jpg";
            HttpWebRequest request = (HttpWebRequest)WebRequest.Create(new Uri(url));
            ServicePointManager.Expect100Continue = false;
            try
            {
                ((HttpWebResponse)request.GetResponse()).Close();
            }
            catch (WebException exception)
            {
                if (exception.Status != WebExceptionStatus.ProtocolError){
                    num++;
                }
                if (exception.Message.IndexOf("500 ") > 0){
                    Response.Write("<script>alert(‘服务器内部错误，无法完成请求，请联系管理 员！‘);</script>");}
                if (exception.Message.IndexOf("401 ") > 0){
                    Response.Write("<script>alert(‘需要身份认证，你没有权限！‘);</script>");}
                if (exception.Message.IndexOf("404")> 0){
                    return num;
                }
            }
            num++;
        }
        return num;
    }