System.Data.SqlClient.SqlConnection cn = new System.Data.SqlClient.SqlConnection();
            cn.ConnectionString = "server=.;database=sms;uid=sa;pwd=;";
            System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand();
             = "select userpwd from tb_user where username='"+txtName.Text+"'";
            cmd.Connection = cn;
            cn.Open();
            System.Data.SqlClient.SqlDataReader sdr = cmd.ExecuteReader();

            while (sdr.Read())
            {
                string userpwd = sdr.GetValue(0).ToString();
               
            }
要求：1.是验证旧密码是否通过（在数据库里有这个图的用户名和，密码等）
       2.要修改新密码（不一致旁边LBL显示）
       3.上述代码还缺少哪些，哪位高手帮我补充下。
           

要是这样的问题   不用上论坛吧    书上就有代码说明    是不是你懒的看啊

            System.Data.SqlClient.SqlConnection cn = new System.Data.SqlClient.SqlConnection();
            cn.ConnectionString = "server=.;database=sms;uid=sa;pwd=;";
            System.Data.SqlClient.SqlCommand cmd = new System.Data.SqlClient.SqlCommand();
             = "select userpwd from tb_user where username='"+txtName.Text+"'";
            cmd.Connection = cn;
            cn.Open();
            System.Data.SqlClient.SqlDataReader sdr = cmd.ExecuteReader();
             string userpwd ="";
            while (sdr.Read())
            {
               userpwd = sdr.GetValue(0).ToString();
                 
            }
            sdr.Close();
            if(userpwd!="")
            {
                if(txtNewPwd!=txtNewAgainPwd)
                {
                    lbl.Text="密码不一致！";
                }
                else
                {
                string sql=string.Format("update tb_user set userpwd='{0}' where username='{1}'",txtNewPwd.Text,txtName.Text);
               
                cmd.ExecuteNonQuery();
                }               
            }
            cn.Close();