GridView DataBinding With Stored Procedure

public partial class StudentMaster : System.Web.UI.Page
{
    SqlConnection con;
    SqlDataAdapter da;
    SqlCommand cmd;

    protected void Page_Load(object sender, EventArgs e)
    {
        if(!Page.IsPostBack)
            bind();
    }
    protected void btnadd_Click(object sender, EventArgs e)
    {
        CallProcedure("I");
    }

    public void bind()
    {
        try
        {
            con = new SqlConnection("");
            con.Open();
            da = new SqlDataAdapter("select * from student_master", con);
            DataSet ds = new DataSet();
            da.Fill(ds, "Students Master");

            if (ds != null && ds.Tables.Count > 0 && ds.Tables[0].Rows.Count > 0)
            {
                GridView1.DataSource = ds.Tables[0];
                GridView1.DataBind();
            }
            else
            {
                GridView1.DataSource = null;
                GridView1.DataBind();
            }
        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
        finally
        {
            con.Close();
        }
    }

    public void CallProcedure(string f)
    {
        con = new SqlConnection("")

        try
        {
            con.Open();


            cmd = new SqlCommand("IU_StudDetails", con);

            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@flag", SqlDbType.VarChar).Value = @f;
            cmd.Parameters.AddWithValue("@stdid", SqlDbType.Int).Value = lblid.Text;
            cmd.Parameters.AddWithValue("@sname", SqlDbType.VarChar).Value = txtname.Text;
            cmd.Parameters.AddWithValue("@marks", SqlDbType.Int).Value = txtmarks.Text;
            cmd.Parameters.AddWithValue("@address", SqlDbType.VarChar).Value = txtaddress.Text;
            

            GridviewBind();

            da = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            da.Fill(dt);
            GridView1.DataSource = dt;
            GridView1.DataBind();    

        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }
        finally
        {
            con.Close();
        }
    }


    protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
    {
        lblid.Text = GridView1.SelectedRow.Cells[1].Text;
        txtname.Text = GridView1.SelectedRow.Cells[2].Text;
        txtmarks.Text = GridView1.SelectedRow.Cells[3].Text;
        txtaddress.Text = GridView1.SelectedRow.Cells[4].Text;
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        CallProcedure("U");
        CallProcedure("S");
    }
    protected void Button2_Click(object sender, EventArgs e)
    {
        CallProcedure("D");
    }

    public void GridviewBind()
    {
         con = new SqlConnection("")

         try
         {
             con.Open();
             cmd = new SqlCommand();
             da = new SqlDataAdapter("IU_StudDetails", con);
             da.SelectCommand.CommandType = CommandType.StoredProcedure;


             da.SelectCommand.Parameters.Add(new SqlParameter("@stdid", SqlDbType.Int));
             da.SelectCommand.Parameters["@stdid"].Value = Convert.ToInt32(lblid.Text);

             da.SelectCommand.Parameters.Add(new SqlParameter("@sname", SqlDbType.VarChar));
             da.SelectCommand.Parameters["@sname"].Value = txtname.Text;

             da.SelectCommand.Parameters.Add(new SqlParameter("@marks", SqlDbType.VarChar));
             da.SelectCommand.Parameters["@marks"].Value = Convert.ToInt32(txtmarks.Text);

             da.SelectCommand.Parameters.Add(new SqlParameter("@address", SqlDbType.VarChar));
             da.SelectCommand.Parameters["@address"].Value = txtaddress.Text;


             DataSet ds = new DataSet();
             da.Fill(ds,"");
             GridView1.DataSource = ds.Tables[0];
             GridView1.DataBind();
             da.Dispose();   
}
         catch (Exception ex)
         {
             Response.Write(ex.Message);
         }
         finally
         {
             con.Close();
         }
    }

}