验证管理员输入的帐号和密码是否正确
在“登录”按钮我写了如下的代码：
private void btnlogin_Click(object sender, EventArgs e)
        {
            if (String.IsNullOrEmpty(txtuser.Text) || String.IsNullOrEmpty(txtpwd.Text))
            { MessageBox.Show("输入帐号/密码再登录", "错误提示"); return; }
            int i, flag = 0;
            label1.Text = null;//密码下面有个lable1，用来显示帐号和密码。
            string str1 = txtuser.Text; string str2 = txtpwd.Text;
            string StrSel = "select * from [db_user]";
            string strRow1 = ""; string strRow2 = "";
            string ConnectStr = "server=localhost;database=ClassDesign;uid=sa;pwd=;";
            SqlConnection MyCon = new SqlConnection(ConnectStr);
            try
            {
                MyCon.Open();
                this.Text = "已连接，正在登录";
            }
            catch (SqlException e1)
            {
                MessageBox.Show("连接失败", "出错");
                return;
            }
            SqlCommand MyCmd = new SqlCommand(StrSel,MyCon);
            SqlDataAdapter MydataAdapter = new SqlDataAdapter();
            MydataAdapter.SelectCommand = MyCmd;
            DataSet MyDs = new DataSet();
            MydataAdapter.Fill(MyDs,"db_user");
            for (i = 0; i < MyDs.Tables["db_user"].Rows.Count; i++)
            {
                strRow1 = MyDs.Tables["db_user"].Rows[i]["user"].ToString();
                label1.Text += strRow1;
                strRow2 = MyDs.Tables["db_user"].Rows[i]["pwd"].ToString();
                label1.Text += strRow2;
                if (str1 == strRow1 && str2 == strRow2)
                { flag = 1; break; }
            }
            if (flag == 1)
            {
                this.Hide();
                FrmMain f = (FrmMain)this.ParentForm;
                f.updataMenu();
            }
            else
            {
                MessageBox.Show("帐号/密码错误","错误提示");
                txtuser.Focus();
            }
        }
明明我输入正确，但就是不肯让我登录，气死了
实在是看不出代码错在哪里

第一张图有点模糊，点击就会看得清楚

谢谢了~问题解决