Search records from database between two dates in ASP.Net

Dear Sir,

need your urgent help to complete my task.

how to make  search function BETWEEN two date using asp c#

namespace sfty1
{
    public partial class smmry_emp : System.Web.UI.Page
    {
        public void CreateConnection()
        {
            SqlConnection _sqlConnection = new SqlConnection(strConnectionString);
            _sqlCommand = new SqlCommand();
            _sqlCommand.Connection = _sqlConnection;
        }
        public void OpenConnection()
        {
            _sqlCommand.Connection.Open();
        }
        public void CloseConnection()
        {
            _sqlCommand.Connection.Close();
        }
        public void DisposeConnection()
        {
            _sqlCommand.Connection.Dispose();
        }
        private string strConnectionString = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        private SqlCommand _sqlCommand;

        public string query, constr;
        public SqlConnection con;

        public void connection()
        {

            constr = ConfigurationManager.ConnectionStrings["constr"].ToString();
            con = new SqlConnection(constr);
            con.Open();

        }
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindGrid();
            }
        }
        
        private void BindGrid()
        {
            string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constr))
            {
                //using (SqlCommand cmd = new SqlCommand("select * from pptlk where cls_flg='N' "))
                using (SqlCommand cmd = new SqlCommand("select DISTINCT a.emp_id,a.emp_nm,a.dept,a.agncy,a.lcn,a.dsc,c.prtcpnt,d.cmplnc,e.ttc,a.dt,a.mnth from nmr a,emp b,pptlk c,sdor d,ttc e  WHERE dt BETWEEN " + txtStartDate.Text + "and" + txtEndDate.Text + ""))
                {
                    using (SqlDataAdapter sda = new SqlDataAdapter())
                    {
                        cmd.Connection = con;
                        sda.SelectCommand = cmd;
                        using (DataTable dt = new DataTable())
                        {
                            sda.Fill(dt);
                            GridView1.DataSource = dt;
                            GridView1.DataBind();
                        }
                    }

                }
            }
        }
        protected void OnPageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            GridView1.PageIndex = e.NewPageIndex;
            BindGrid();
        }
    }
}