Delete functionality does not work in disconnected mode

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 Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection("Data Source=AMMA-PC\\SQLEXPRESS;Initial Catalog=E_learn;Integrated Security=True");       
        SqlDataAdapter da = new SqlDataAdapter();
        SqlCommand cmd = new SqlCommand("select * from Student where sid=@sid",con);
        cmd.Parameters.Add("@sid", SqlDbType.Int).Value = TextBox1.Text;
        da.SelectCommand = cmd;
        DataSet ds = new DataSet();
        da.Fill(ds);
        if (ds.Tables[0].Rows.Count > 0)
        {
            DataRow dr = ds.Tables[0].Rows[0];
            TextBox1.Text = dr[0].ToString();
            TextBox2.Text = dr[1].ToString();
            TextBox3.Text = dr[2].ToString();

        }
        else
        {
            Response.Write("Record not found");
        }
       
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection("Data Source=AMMA-PC\\SQLEXPRESS;Initial Catalog=E_learn;Integrated Security=True");
        SqlDataAdapter da = new SqlDataAdapter("select * from Student", con);
        DataSet ds = new DataSet();
        da.Fill(ds, "Student");
        SqlCommand insert = new SqlCommand("insert into Student values(@sid,@sname,@marks)", con);
        insert.Parameters.Add("@sid", SqlDbType.Int).Value = TextBox1.Text;
        insert.Parameters.Add("@sname", SqlDbType.VarChar, 50).Value = TextBox2.Text;
        insert.Parameters.Add("@marks", SqlDbType.Int).Value = TextBox3.Text;
        da.InsertCommand = insert;
        DataTable dt = ds.Tables[0];
        DataRow dr = dt.NewRow();
        dr[0] = TextBox1.Text;
        dr[1] = TextBox2.Text;
        dr[2] = TextBox3.Text;
        dt.Rows.Add(dr);
        da.Update(ds, "Student");
        Response.Write("inserted successfully");
    }
    protected void Button3_Click(object sender, EventArgs e)
    {
        SqlConnection con = new SqlConnection("Data Source=AMMA-PC\\SQLEXPRESS;Initial Catalog=E_learn;Integrated Security=True");
        SqlDataAdapter da = new SqlDataAdapter("select * from Student", con);
        DataSet ds = new DataSet();
        da.Fill(ds, "Student");
        SqlCommand update = new SqlCommand("Update Student set sname = @sname where sid = @sid", con);
        update.Parameters.Add("@sname", SqlDbType.VarChar, 50).Value = TextBox2.Text;
        update.Parameters.Add("@sid", SqlDbType.Int).Value = TextBox1.Text;
        da.UpdateCommand = update;
        if (ds.Tables[0].Rows.Count > 0)
        {
            DataRow r = ds.Tables[0].Rows[0];
            r[0] = TextBox1.Text;
            r[1] = TextBox2.Text;
            da.Update(ds, "Student");
            Console.WriteLine("Updated sucessfully");
        }

    }
    protected void Button4_Click(object sender, EventArgs e)
    {

        SqlConnection con = new SqlConnection("Data Source=AMMA-PC\\SQLEXPRESS;Initial Catalog=E_learn;Integrated Security=True");
        SqlDataAdapter da = new SqlDataAdapter("select * from Student", con);
        DataSet ds = new DataSet();
        da.Fill(ds, "Student");
        SqlCommand delete = new SqlCommand("delete from Student where sid=@sid", con);
        delete.Parameters.Add("@sid", SqlDbType.Int).Value = TextBox1.Text; 
        da.DeleteCommand = delete;
        if (ds.Tables[0].Rows.Count > 0)
        {
            DataTable dt = ds.Tables[0];
            DataColumn[] Columns = new DataColumn[1];
            Columns[0] = dt.Columns["sid"];
            dt.PrimaryKey = Columns;
            DataRow dr = dt.Rows[0];
            if(dr[0]==TextBox1.Text )
            {
                dr.Delete();
                dt.AcceptChanges();
            }
            
           da.Update(ds, "Student");
           Response.Write("deleted successfully");

        }

    }
}