I need the proper validation in the registration page in this 3-tier architecture

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;

namespace ors_grad_.DAL
{
    class register
    {
     
        SqlConnection sqlcon;
        SqlCommand sqlcmd;
        string Output;
        public void connect()
        {
            try
            {
                sqlcon = new SqlConnection(@"Data Source=server;Initial Catalog=database;User ID=sa;Password=admin");
                sqlcon.Open();
            }
            catch (SqlException sqlerror)
            {
                foreach (SqlError e in sqlerror.Errors)
                {
                    Output = e.Message;
                }
            }
        }
        public string signUp(BLL.Register bl)
        {
            connect();
            int  uid = bl.UserId;
            string fname = bl.F_Name;
            string lname = bl.L_Name;
            string gender = bl.Gender;
            DateTime dob = bl.Dob;
            string pwd = bl.Password;
            string confirmpwd = bl.Con_Password;
            string phoneno = bl.Phone_No;
            string securityqn = bl.Security_Qn;
            string ans = bl.Ans;
            string email = bl.Email;
            string degree = bl.Degree;
            try
            {
                sqlcmd = new SqlCommand("dbo.sp_reg", sqlcon);
                sqlcmd.CommandType = CommandType.StoredProcedure;
                sqlcon.InfoMessage += new SqlInfoMessageEventHandler(Con_InfoMessage);

                sqlcmd.Parameters.AddWithValue("@userid", uid);
                sqlcmd.Parameters.AddWithValue("@fname", fname);
                sqlcmd.Parameters.AddWithValue("@lname", lname);
                sqlcmd.Parameters.AddWithValue("@gender", gender);
                sqlcmd.Parameters.AddWithValue("@dob", dob);
                sqlcmd.Parameters.AddWithValue("@password", pwd);
                sqlcmd.Parameters.AddWithValue("@phno", phoneno);
                sqlcmd.Parameters.AddWithValue("@degree", degree);
                sqlcmd.Parameters.AddWithValue("@securityqn", securityqn);
                sqlcmd.Parameters.AddWithValue("@answer", ans);
                sqlcmd.Parameters.AddWithValue("@email", email);
                //sqlcmd.Parameters.AddWithValue("@Type", type);
                sqlcmd.ExecuteNonQuery();
            }
            catch (SqlException sqlerror)
            {
                foreach (SqlError e in sqlerror.Errors)
                {
                    Output = e.Message;
                }
            }
            return Output;
        }
        public void Con_InfoMessage(object sender, SqlInfoMessageEventArgs args)
        {
            Output = args.Message;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ors_grad_.BLL
{
    class Register
    {
        private int userId;
        private string f_name;
        private string l_Name;
        private string gender;
        private DateTime dob;
        private string password;
        private string con_Password;
        private string phone_No;
        private string security_Qn;
        private string ans;
        private string email;
        private string degree;
        
        public int UserId
        {
            get { return userId; }
            set { userId = value; }
        }
        public string F_Name
        {
            get { return f_name; }
            set { f_name = value; }
        }
        public string L_Name
        {
            get { return l_Name; }
            set { l_Name = value; }
        }
        public string Gender
        {
            get { return gender; }
            set { gender = value; }
        }

        public DateTime Dob
        {
            get { return dob; }
            set { dob = value; }
        }
        public string Password
        {
            get { return password; }
            set { password = value; }
        }
        public string Con_Password
        {
            get { return con_Password; }
            set { con_Password = value; }
        }
        public string Phone_No
        {
            get { return phone_No; }
            set { phone_No= value; }
        }
        public string Security_Qn
        {
            get { return security_Qn; }
            set { security_Qn = value; }
        }
        public string Ans
        {
            get { return ans; }
            set { ans = value; }
        }
        public string Email
        {
            get { return email; }
            set { email = value;}
        }
        public string Degree
        {
            get { return degree; }
            set { degree = value; }
        }
        public int random()
        {
            Random rnd = new Random();
            UserId = rnd.Next(1111, 9999);
            return UserId;
            
        }
        DAL.register su = new DAL.register();
        public string signUp1()
        {
            return su.signUp(this);
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;

namespace ors_grad_.DAL
{
    class Appstatus
    {
        SqlConnection con;
        public static string status;
        public void connect()
        {
            con = new SqlConnection(@"Data Source =server;uid=sa;password=admin;Initial Catalog =ORSgrad");
            con.Open();
        }
        public int update_status1(string appid,string status)
        {
            connect();
            status = "Processing";
            string str = "update app_status set Status='"+status+"' where AppID='" + appid + "'";
            SqlCommand cmd = new SqlCommand(str, con);
            //con.Open();
            int i = cmd.ExecuteNonQuery();
            con.Close();
            if (i == 0)
                return 1;
            else if (i == 1)
                return 2;
            return 0;
        }

        public DataSet view_all1()
        {
            //pw.tab
            connect();
            SqlCommand cmd = new SqlCommand("select * from app_status where Status='"+status+"'", con);
                        
           // con.Open();
            SqlDataAdapter adp = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            adp.Fill(ds);
            return ds;
            con.Close();
        }
        public SqlDataReader user_detail1()
        {
            connect();
            string str = "select distinct userid from grad_details";
            SqlDataReader dr = null;
            SqlCommand cmd = new SqlCommand(str, con);
            dr = cmd.ExecuteReader();
            return dr;
            con.Close();
        }
        public DataSet view_user_details1(string uid)
        {
            connect();
            string str = "select * from app_status where UserId='" + uid + "'";
            SqlCommand cmd = new SqlCommand(str, con);
            SqlDataAdapter adp = new SqlDataAdapter(cmd);
            DataSet ds = new DataSet();
            adp.Fill(ds);
            return ds;
        }
        public SqlDataReader app_track1(string appid)
        {
            connect();
            SqlCommand cmd = new SqlCommand("Sp_TrackApp", con);
            cmd.CommandType = CommandType.StoredProcedure;
            cmd.Parameters.AddWithValue("@appid", appid);
            SqlDataReader dr = cmd.ExecuteReader();
            //con.Close();
            return dr;
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;

namespace ors_grad_.BLL
{
    class Appstatus
    {
        DAL.Appstatus ad = new DAL.Appstatus();
        public int update_status(string appid,string status)
        {
            if (appid == "")
                return 0;
            else
                return ad.update_status1(appid,status);
        }
        public DataSet view_all()
        {
            return ad.view_all1();
        }
        public SqlDataReader user_detail()
        {
            return ad.user_detail1();
        }
        public DataSet view_user_details(string uid)
        {
                 return ad.view_user_details1(uid);
        }
        public SqlDataReader app_track(string uid)
        {
            return ad.app_track1(uid);
        }
    }
}