如何得到索引-datatable号 目的:使每个登陆的人修改自己的密码

        private void btn_changkey_btn_ok_Click(object sender, EventArgs e)
        {
            if (txt_changkey_newkey.Text.Trim() != "" & txt_changekey_oldkey.Text.Trim() != "" & txt_changekey_conform.Text.Trim() != "")
            {
                MyClass.MyMeans.getcon();
                MyClass.MyMeans.Mean_SQL = "select * from UserDefine";
                SqlDataAdapter da = new SqlDataAdapter(MyClass.MyMeans.Mean_SQL,MyClass.MyMeans.Conn);
                SqlCommandBuilder sqlcomb = new SqlCommandBuilder(da);
                DataSet ds = new DataSet();
                da.Fill(ds, "UserDefine");

                //ds.Tables["UserDefine"].Rows.Find(MyClass.MyMeans.UserName); 

                //我该怎么得到我要的哪行的索引
                ds.Tables["UserDefine"].Rows[0]["PassWord"] = txt_changekey_conform.Text;
                da.Update(ds, "UserDefine");
                MessageBox.Show("密码修改成功", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                mym.con_close();
                this.Close();
            }
            else
            {
                MessageBox.Show("信息填写不全", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
            }

 

        }

//为登陆的用户修改密码，我每次只能修改第一行数据的密码，我不会操作 XML 不知道怎么去检索，我要针对的其他的人的对应的密码.

UserID     UserName             PassWord                                           detail                                                                                              
---------- -------------------- --------------------------------------------------
001        jack                 admin                                              NULL
002        mary                 666666                                             NULL