谁能用c#帮我翻译下面的代码？原来是用vb语言写的

Question

Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        If Page.IsValid Then
            Dim conn As SqlConnection
            conn = New SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=|datadirectory|Database.mdf;Integrated Security=True;User Instance=True")
            conn.Open()
            Dim cmdstr As String
            cmdstr = "select * from [User]  where name ='" + TextBox1.Text.Trim() + "'and ps = '" + TextBox2.Text.Trim() + "'and flag='" + DropDownList1.SelectedIndex.ToString() + "'"
            
            Dim cmd As SqlCommand
            cmd = New SqlCommand(cmdstr, conn)
            Dim sdr As SqlDataReader = cmd.ExecuteReader()
            If sdr.read() Then
                If DropDownList1.SelectedIndex.ToString() = "0" Then
                    Session("flag") = "普通用户"
                    Session("name") = TextBox1.Text
                    Response.Redirect("index.aspx")
                ElseIf DropDownList1.SelectedIndex.ToString() = "1" Then
                    Session("flag") = "管理员"
                    
                    Response.Redirect("indexmanager.aspx")
                End If
                
            Else
                MsgBox("您输入用户名或者密码有误！", MsgBoxStyle.OkOnly)
                TextBox1.Text = ""
                TextBox2.Text = ""
            End If
            conn.Close()            Response.Redirect("index.aspx")
        
        End If
        
    End Sub

Answer 1

 if (Page.IsValid)
            {
                SqlConnection conn;
                conn = new SqlConnection(@"Data Source=.\SQLEXPRESS;AttachDbFilename=|datadirectory|Database.mdf;Integrated Security=True;User Instance=True");
                conn.Open();
                string cmdstr="";
                cmdstr="select * from [User] where name ='" + TextBox1.Text.Trim() + "'and ps = '" + TextBox2.Text.Trim() + "'and flag='" + DropDownList1.SelectedIndex.ToString() + "'";
                SqlCommand cmd;
                cmd=new SqlCommand(cmdstr,conn);
                SqlDataReader sdr=cmd.ExecuteReader();
                if(sdr.Read())
                {
                    if(DropDownList1.SelectedIndex.ToString() == "0")
                    {
                        Session("flag") = "普通用户";
                        Session("name") = TextBox1.Text;
                        Response.Redirect("index.aspx");
                    }
                    else if (DropDownList1.SelectedIndex.ToString() == "1")
                    {
                        Session("flag") = "管理员";
                        Response.Redirect("indexmanager.aspx");
                    }
                    else
                    {
                        MessageBox.Show("您输入用户名或者密码有误！", "提示", MessageBoxButtons.OK);
                        TextBox1.Text = "";
                        TextBox2.Text = "";
                    }
                }
               
            }
            conn.Close();
            Response.Redirect("index.aspx");

Answer 2

楼上正解，分数给你啦，还有一小段，希望可以帮我再翻译一下
  Dim b As SqlConnection
        Dim time As DateTime
        b = New SqlConnection("Data Source=.\SQLEXPRESS;AttachDbFilename=|datadirectory|database.mdf;Integrated Security=True;User Instance=True")
        b.Open()
        time = Now()
        If TextBox1.Text = "" Then
            Label1.Text = "请输入您的昵称!"
        ElseIf TextBox2.Text = "" Then
            Label1.Text = "请输入您的E-mail!"
        Else
            Dim cmdst As String
            Dim cmd As SqlCommand
            cmdst = "insert into guestbook values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "','" + time + "')"
            cmd = New SqlCommand(cmdst, b)
            cmd.ExecuteNonQuery()
            b.Close()
            MsgBox("留言成功！", MsgBoxStyle.OkOnly)
            Response.Redirect("guest.aspx")        End If    End Sub