Need Urgent Help i cannot access value dynamic dropdownlist

[Anant]

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;
 
public partial class assigned : System.Web.UI.Page
{
    DropDownList d;
    DropDownList dr;
    protected void Page_Load(object sender, EventArgs e)
    {
 
    }
    protected void TextBox4_TextChanged(object sender, EventArgs e)
    {
        
 
    }       
    
    protected void Button1_Click(object sender, EventArgs e)
    {
        int a = Convert.ToInt32(TextBox1.Text);
       
        try
        {  
           
            for (int i = 0; i < a; i++)
            {
                d = new DropDownList();
                d.ID = "Text" + i;
                LiteralControl l1 = new LiteralControl("<br></br>");
              
                d.Items.Add("Rahul");
                d.Items.Add("Gautum");
                d.Items.Add("anant");                
               
                Panel3.Controls.Add(d);
                Panel3.Controls.Add(l1);          
                
            }
            
        }
        catch (Exception e1)
        {
            Label4.Text = "" + e1.Message.ToString();
        }
    }
  
 
    protected void Button2_Click(object sender, EventArgs e)
    {
 
  
      int a = Convert.ToInt32(TextBox1.Text);
            string value = "";
            for (int i = 0; i < a; i++)
            {
                string str  ="Text" + i;
                dr = new DropDownList();
                dr = (DropDownList)(Panel3.FindControl(str));
               
                value = dr.SelectedValue.ToString();
                     SqlConnection con = new SqlConnection("Data Source=ABC-0D78787890A;Initial Catalog=Amit;Integrated Security=True");
               
                con.Open();
 
                SqlCommand cmd1 = new SqlCommand("insert into niitstud values('" + value + "')", con);
                cmd1.ExecuteNonQuery();
                con.Close();
               
                
            }
                
            }
 
    }
}