date difference between two dates in c#.net code

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data; //  namespace for gridview
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient; //namespace for sqlconnection

namespace retrive_data_by_using_datetime
{
    public partial class Form1 : Form
    {
        public DateTime dt;
        public Form1()
        {
            InitializeComponent();
        }
//connection string
        SqlConnection con = new SqlConnection("Data Source=USER-PC;Initial Catalog=student;Integrated Security=True");
//insert date into the database using date time picker
        private void button1_Click(object sender, EventArgs e)
        {
            con.Open();
//here i am using  datetime picker for inserting date
            dt = Convert.ToDateTime(dateTimePicker1.Text);
            SqlCommand cmd = new SqlCommand("insert into tbl_Date values('"+dt+"')", con);
            int r = cmd.ExecuteNonQuery();
            if (r >0)
            {
                MessageBox.Show("saved successfully");
            }
            con.Close();
        }
//retrive (intermediate dates fromdate and todate) date from database and display in gridview
//in datebase when u create specify the datatype datetime
        private void button2_Click(object sender, EventArgs e)
        {
            string from = Convert.ToString(dtpfrom.Text);
            string to = Convert.ToString(dtpto.Text);
            DateTime fromdate = Convert.ToDateTime(from);
            DateTime todate = Convert.ToDateTime(to);
//sqlcommand for retrive date from date base
            SqlCommand cmd = new SqlCommand("select datea from tbl_Date where datea between convert(date,'"+fromdate.ToLocalTime()+"',0)and convert(date,'"+todate.ToLocalTime()+"',0)", con);
            SqlDataAdapter ad = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            ad.Fill(dt);
            dataGridView2.DataSource = dt;
           }
    }
}