如何实现这样的字符串连接

怎么实现这样的字符串连接？
DataTable dt = HcPBCommBLL.GetHcPBGroupCatalogID(hashtable)

我有一数据表(dt)读出来的数据如下：

row catalog_id

1 41
2 21
3 55
4 33

怎么把列catalog_id的数据连接成 string id="41,21,55,33"

谢谢

[解决办法]
String id=""
for (int i=0;i<=dt.Rows.count-1;i++
{
id=id & dt.Row[i][1] & ",";
}
id=id.TrimEnd(",");
[解决办法]

C# code

DataTable dt = new DataTable("image");        DataColumn dc1, dc2;        dc1 = new DataColumn("row", System.Type.GetType("System.Int32"));        dc1.AutoIncrement = true;        dc1.AutoIncrementSeed = 1;        dc1.AutoIncrementStep = 1;        dt.Columns.Add(dc1);        dc2 = new DataColumn("catalog_id", System.Type.GetType("System.Int32"));        dt.Columns.Add(dc2);        DataRow dr1 = dt.NewRow();        dr1["catalog_id"] = 41;        dt.Rows.Add(dr1);        DataRow dr2 = dt.NewRow();        dr2["catalog_id"] = 21;        dt.Rows.Add(dr2);        DataRow dr3 = dt.NewRow();        dr3["catalog_id"] = 55;        dt.Rows.Add(dr3);        DataRow dr4 = dt.NewRow();        dr4["catalog_id"] = 33;        dt.Rows.Add(dr4);        GridView1.DataSource = dt;        GridView1.DataBind();        string id = "";        for (int i = 0, max = dt.Rows.Count; i < max; i++)        {            id += dt.Rows[i]["catalog_id"].ToString() + ",";        }        id = id.Substring(0, id.Length - 1);        Response.Write(id);
[解决办法]
 string PurviewIdstr = ",";
                       for (int j = 0; j < cb_purview.Items.Count; j++)
                       {
                           if (cb_purview.SelectedValue == "")
                           {
                               HongShangProject.Common.MessageBox.Show(this, "未选择任何权限,请选择！");
                           }
                           else
                           {
                               if (cb_purview.Items[j].Selected)
                               {
                                   int _pid = 0;
                                   int.TryParse(cb_purview.Items[j].Value.Trim(), out _pid);
                                   PurviewIdstr += _cid + "-" + _pid + ",";
                               }
                           }
                       }
[解决办法]
缺少
C# code
using System.Data;