How to Auto Generate Registration Random Number fill the Form

-------First create Table for Database-----

-------------source Code For Design Code--------

----------RagistrationPage Aspx code---------

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Data;

using System.Data.SqlClient;

public partial class _Default : System.Web.UI.Page

{

 SqlConnection con =new SqlConnection("Data Source=.;Initial Catalog=adonetpractices;Integrated Security=True");

    protected void Page_Load(object sender, EventArgs e)

    {

    }

    protected void Button1_Click(object sender, EventArgs e)

    {

        string regno = "";

        regno = TextBox1.Text.Trim().Substring(0, 2).ToUpper();

        regno += DateTime.Now.Day.ToString() + DateTime.Now.Month.ToString() + DateTime.Now.Year.ToString();

        Random rr = new Random();

        regno += rr.Next().ToString();

        con.Open();

       

        SqlCommand cmd = new SqlCommand("insert into employee values(@regno,@Name,@email,@mobile,@gender,@dob,@photo,@state,@city,@course)", con);

        cmd.Parameters.AddWithValue("@regno", regno);

        cmd.Parameters.AddWithValue("@name", TextBox1.Text);

        cmd.Parameters.AddWithValue("@email", TextBox2.Text);

        cmd.Parameters.AddWithValue("@mobile", TextBox3.Text);

        cmd.Parameters.AddWithValue("@gender", RadioButtonList1.SelectedItem.Text);

        cmd.Parameters.AddWithValue("@dob", TextBox4.Text);

        cmd.Parameters.AddWithValue("@photo", FileUpload1.FileName);

        cmd.Parameters.AddWithValue("@state", DropDownList1.SelectedItem.Text);

        cmd.Parameters.AddWithValue("@city", DropDownList2.SelectedItem.Text);

        cmd.Parameters.AddWithValue("@course", CheckBoxList1.SelectedItem.Text);

        string course = "";

        foreach (ListItem li in CheckBoxList1.Items)

        {

            if (li.Selected)

            {

                course +=li.Text ;

            }

        }

        course = course.Remove(course.Length - 1);

        int i = cmd.ExecuteNonQuery();

        if (i == 1)

        {

            Response.Write("<script>alert('" + regno + "')</script>");

        }

        else

        {

            Response.Write("<script>alert('data not submit')</script>");

        }

        con.Close();

       

    }

}

-------Result------