how to check userid and password from database.i have to open a page of teacher,admin,parent through switch case

how to check userid and password from database.i have to open a page of teacher,admin,parent through switch case

my code is here:................

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;
using System.Configuration;

public partial class _Default : System.Web.UI.Page
{
    SqlConnection con;
    SqlDataReader dr;
    SqlDataReader dr1,dr2;
    SqlDataAdapter da;
    SqlCommand sqlcomm;
    string username;
    string password;
    protected void Page_Load(object sender, EventArgs e)
    {
        string str = (string)ConfigurationManager.AppSettings["connectionstring"];
        con = new SqlConnection(str);
    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        con.Open();
        string s=selected(DropDownList1.SelectedValue);
        string p="select username,password from login where type="+ s +"";
        sqlcomm = new SqlCommand(p,con);
        dr=sqlcomm.ExecuteReader();
        if (dr.Read())
        {
            username = dr1.GetString(0);
            password = dr2.GetString(1);
            if ((TextBox0.Text == username)&&(TextBox1.Text==password))
            {
                Server.Transfer("Admin.aspx");
                switch ()
                {
                    case "Admin":
                        return "Admin.aspx";
                    case "Parent":
                        return "Parent.aspx";
                    case "Teacher":
                        return "Teacher.aspx";
                    default:
                        return "zero";

                }
            }
        \
        }
       
    }
    public string selected(string i)
    {

        switch (i)
        {
            case "Admin":
                return "Admin";
            case "Parent":
                return "Parent";
            case "Teacher":
                return "Teacher";
            default :
                return "zero";
          
        }
    }
}