ASP.NET

public class Example {
  public string Name { get; set; }
  public DateTime Expires { get; set; }
}

var examples = getExamples();
for each example in examples {
  example.Expires.AddDays(30);
}

FetchDetails

public DataTable FetchDetails()
{
    con.Open();
    DataTable dt = new DataTable();
    using(SqlCommand cmd = new SqlCommand("spfetchdetail", con))
    {
        cmd.CommandType = CommandType.StoredProcedure;
        cmd.Parameters.AddWithValue("@pid", pid);
        
        SqlDataAdapter sda = new SqlDataAdapter(cmd);
        sda.Fill(dt);
    }
    return dt.Table[0];
}

public DataTable fetchdetail()
{
    return dll.FetchDetails(); // Call to your DAL returning Datatable
}

protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
    string pid = ""; string pname = ""; string pcid = ""; string sdesc = ""; string desc = ""; string qty = ""; string prce = ""; string len = "";
    DataTable dt = bll.fetchdetail(); // Call to BAL and reveice datatable
    // extract the data from this datatable now to populate your variables now
    HiddenField1.Value = pid;
    txt_proName.Text = pname;
    ddl_category.SelectedValue = pcid;
    txt_sdesc.Text = sdesc;
    txt_ldesc.Text = desc;
    txt_qnty.Text = qty;
    txt_price.Text = prce;
    txt_len.Text = len; 
}