DAL Class

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;

///

/// Summary description for DAL
///

    public class DAL
    {
        SqlConnection con;
        SqlCommand cmd;
        SqlDataAdapter sda;
        String ConString;


        public DAL()
        {
            ConString = ConfigurationManager.ConnectionStrings["ConnString"].ConnectionString;
            con = new SqlConnection(ConString);
        }

        public void ConnectionOpen()
        {
            if (con.State == ConnectionState.Closed)
            {
                con.Open();
            }
        }
        public void ConnectionClose()
        {
            if (con.State == ConnectionState.Open)
            {
                con.Close();
            }
        }


        public DataTable GetDataTable(String query)
        {
            con.Open();
            sda = new SqlDataAdapter(query, con);
            DataTable dt = new DataTable();
            sda.Fill(dt);
            return dt;
        }





        public int PutData(String query)
        {
            cmd = new SqlCommand();
            cmd.CommandText = query;
            cmd.Connection = con;

            con.Open();
            int a = cmd.ExecuteNonQuery();
            con.Close();
            return a;
        }

        public string ExecuteScaler(String query)
        {
            cmd = new SqlCommand();
            cmd.CommandText = query;
            cmd.Connection = con;

            con.Open();
            string s = Convert.ToString(cmd.ExecuteScalar());
            con.Close();

            return s;
        }


        public void FillCombo(DropDownList ddl, String query, String item, String Value, String ZerothElemnt, int SelectedIndex)
        {
            DataTable dt = new DataTable();
            dt = GetDataTable(query);
            ddl.DataSource = dt;
            ddl.DataTextField = item;
            ddl.DataValueField = Value;
            ddl.DataBind();
            ddl.Items.Insert(0, ZerothElemnt);
            ddl.SelectedIndex = SelectedIndex;
        }


        public void FillCombo(DropDownList ddl, String query, String item, String Value, int SelectedIndex)
        {
            DataTable dt = new DataTable();
            dt = GetDataTable(query);
            ddl.DataSource = dt;
            ddl.DataBind();
            ddl.SelectedIndex = SelectedIndex;
        }


        public void FillGrid(GridView grd, String query)
        {
            DataTable dt = new DataTable();
            dt = GetDataTable(query);
            grd.DataSource = dt;
            grd.DataBind();
        }

        public void FillDetailView(DetailsView dv, String query)
        {
            DataTable dt = new DataTable();
            dt = GetDataTable(query);
            dv.DataSource = dt;
            dv.DataBind();
        }
    }

Other DAL

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Data.SqlClient;

///

/// Summary description for DAL
///

public class DAL
{

    public SqlConnection con = new SqlConnection(@"Data Source=localhost\SQLEXPRESS;initial Catalog=Demo1;integrated security=true;");
    public SqlCommand cmd = new SqlCommand();
    public SqlDataAdapter adp = new SqlDataAdapter();
    public DataSet ds = new DataSet();
    public DataTable dt = new DataTable();

   public  string sqlstr;
    public DAL()
     
    {
        //
        // TODO: Add constructor logic here
        //
    }
  
    public void conopen()
    {
        if (con.State == ConnectionState.Closed)
            con.Open();
    }
    public void insertfun(string str)
    {
        conopen();
        cmd.Connection = con;
        cmd.CommandText = str;
        adp.InsertCommand = cmd;
        cmd.CommandType = CommandType.Text;
        cmd.ExecuteNonQuery();
    }
    public void Updatefun(string str)
    {
        conopen();
        cmd.Connection = con;
        cmd.CommandText = str;
        cmd.CommandType = CommandType.Text;
        adp.UpdateCommand = cmd;
        cmd.ExecuteNonQuery();
    }
    public void Deletefun(string str)
    {
        conopen();
        cmd.Connection = con;
        cmd.CommandText = str;
        cmd.CommandType = CommandType.Text;
        adp.DeleteCommand = cmd;
        cmd.ExecuteNonQuery();

    }
  
    public DataTable getdatafun(string str)
    {
        conopen();
        cmd.Parameters.Clear();
        cmd.Connection = con;
        cmd.CommandText = str;
        cmd.CommandType = CommandType.Text;
        adp.SelectCommand = cmd;
        try
        {
            dt.Clear();
            dt.Columns.Clear();
        }
        catch (Exception ex)
        { }
        adp.Fill(dt);
        //dt.Clear();
        return dt;

    }
    public static void Filldrowp(DropDownList ddl, DataTable dt, string datamember, string datavalue)
    {
        try
        {
            ddl.DataSource = dt;
            ddl.DataTextField = datamember;
            ddl.DataValueField = datavalue;
            ddl.DataBind();
            ddl.Items.Insert(0, "---Select---");
        }
        catch (Exception ex)
        {
        }
    }


    public void fillcombo(DropDownList drp, string display, string values, string qury)
    {
        conopen();
        cmd.Connection = con;
        cmd.Parameters.Clear();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = qury;
        adp.SelectCommand = cmd;
        try
        {
            dt.Clear();
        }
        catch (Exception ex)
        { }
        adp .Fill (dt);
            if (dt.Rows .Count >0)
            {
                int i;
                for (i=0;i
                {
                    //drp.DataValueField = dt.Rows[0][values].ToString();
                    //drp.DataTextField = dt.Rows[0][display].ToString();
                    drp.DataValueField = dt.Rows[i][values].ToString();
                    drp.DataTextField = dt.Rows[i][values].ToString();
                    drp.Items.Add(dt.Rows[i][display].ToString());
                }
                {
                    drp .DataBind ();
                }

    }

   

}
    public void FillCobobox(DropDownList DDL, string Dislay, string values, string quary)
    {
        conopen();
        cmd.Parameters.Clear();
        cmd.Connection = con;
        cmd.CommandText = quary;
        cmd.CommandType = CommandType.Text;
        adp.SelectCommand = cmd;
        try
        {
            dt.Clear();
        }
        catch (Exception ex)
        { }
        adp.Fill(dt);
        if (dt.Rows.Count > 0)
        {
            DDL.DataValueField = dt.Rows[0][Dislay].ToString();
            DDL.DataTextField = dt.Rows[0][values].ToString();
        }
        {
            DDL.DataBind();
        }
    }

        public void fillcombo(System.Windows.Forms.ComboBox cmbo, string display, string value, string sqlstr)
        {
            DataTable dtcombo = new DataTable();
            conopen();
            cmd.CommandText = sqlstr;
            cmd.Connection = con;
            cmd.CommandType = CommandType.Text;
            adp.SelectCommand = cmd;
            adp.Fill(dtcombo);
            cmbo.DataSource = dtcombo;
            cmbo.ValueMember = dtcombo.Columns[value].ToString();
           // cmbo.DisplayMember = dtcombo.Columns[display].ToString();
    
        }

    }
}

}