Get data based on DropDownList Selection and display in TextBox in ASP.Net

I am selecting the Address from Table based on Selected Value of DropDownList. Value here is the Id of table.

HTML:

Select Name
        <asp:DropDownList ID="ddlEmployees" runat="server" AutoPostBack="true" OnSelectedIndexChanged="OnSelectedIndexChanged_ddlEmployees">
        </asp:DropDownList>
        <br />
        <asp:TextBox ID="txtAddress" runat="server" TextMode="MultiLine" />

C#:

protected void Page_Load(object sender, EventArgs e)
        {
            if (!this.IsPostBack)
            {
                this.PopulateDropDownList();
            }
        }

        private void PopulateDropDownList()
        {
            string constr = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constr))
            {
                using (SqlCommand cmd = new SqlCommand("SELECT FirstName,EmployeeID FROM Employees", con))
                {
                    using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                    {
                        con.Open();
                        DataSet ds = new DataSet();
                        da.Fill(ds);
                        this.ddlEmployees.DataTextField = "FirstName";
                        this.ddlEmployees.DataValueField = "EmployeeID";
                        this.ddlEmployees.DataSource = ds;
                        this.ddlEmployees.DataBind();
                        this.ddlEmployees.Items.Insert(0, new System.Web.UI.WebControls.ListItem("Please Select", "0"));
                    }
                }
            }
        }

        protected void OnSelectedIndexChanged_ddlEmployees(object sender, EventArgs e)
        {
            if (this.ddlEmployees.SelectedItem.Value != "0")
            {
                string constr = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
                using (SqlConnection con = new SqlConnection(constr))
                {
                    using (SqlCommand cmd = new SqlCommand("SELECT Address FROM Employees WHERE EmployeeID = @EmployeeID", con))
                    {
                        using (SqlDataAdapter da = new SqlDataAdapter(cmd))
                        {
                            cmd.Parameters.AddWithValue("@EmployeeID", this.ddlEmployees.SelectedItem.Value);
                            con.Open();
                            object address = cmd.ExecuteScalar();
                            con.Close();
                            this.txtAddress.Text = address.ToString();
                        }
                    }
                }
            }
            else
            {
                this.txtAddress.Text = "Please Select Name from List";
            }
        }

VB:

Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
        If Not Me.IsPostBack Then
            Me.PopulateDropDownList()
        End If
    End Sub

    Private Sub PopulateDropDownList()
        Dim constr As String = ConfigurationManager.ConnectionStrings("conString2").ConnectionString
        Using con As New SqlConnection(constr)
            Using cmd As New SqlCommand("SELECT FirstName,EmployeeID FROM Employees", con)
                Using da As New SqlDataAdapter(cmd)
                    con.Open()
                    Dim ds As New DataSet()
                    da.Fill(ds)
                    Me.ddlEmployees.DataTextField = "FirstName"
                    Me.ddlEmployees.DataValueField = "EmployeeID"
                    Me.ddlEmployees.DataSource = ds
                    Me.ddlEmployees.DataBind()
                    Me.ddlEmployees.Items.Insert(0, New System.Web.UI.WebControls.ListItem("Please Select", "0"))
                End Using
            End Using
        End Using
    End Sub

    Protected Sub OnSelectedIndexChanged_ddlEmployees(sender As Object, e As EventArgs)
        If Me.ddlEmployees.SelectedItem.Value <> "0" Then
            Dim constr As String = ConfigurationManager.ConnectionStrings("conString2").ConnectionString
            Using con As New SqlConnection(constr)
                Using cmd As New SqlCommand("SELECT Address FROM Employees WHERE EmployeeID = @EmployeeID", con)
                    Using da As New SqlDataAdapter(cmd)
                        cmd.Parameters.AddWithValue("@EmployeeID", Me.ddlEmployees.SelectedItem.Value)
                        con.Open()
                        Dim address As Object = cmd.ExecuteScalar()
                        con.Close()
                        Me.txtAddress.Text = address.ToString()
                    End Using
                End Using
            End Using
        Else
            Me.txtAddress.Text = "Please Select Name from List"
        End If
    End Sub

Import Namespace:

Imports System.Configuration
Imports System.Data.SqlClient
Imports System.Data

Image:

Thank You.