注册个人觉得只有操作员具有此功能，所以放在了操作员的权限当中。

UI层

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data;

namespace UI
{
    public partial class FrmLogon : Form
    {
        public FrmLogon()
        {
            InitializeComponent();
        }

        private void btLogon_Click(object sender, EventArgs e)
        {
            if (txtCardno.Text=="" || txtCharge.Text=="" || txtIdentity.Text=="" ||txtName.Text=="" || txtPwd.Text=="" || comboBox1.Text=="")
            {
                MessageBox.Show("请您将注册信息填写完整", "温馨提示");
            }
            else
            {
                //student表
                Facade.StudentFacade facade = new Facade.StudentFacade();//实例化外观层
                Entity.Student_Info stu = new Entity.Student_Info();//实例化学生实体
                stu.cardno = txtCardno.Text.Trim();//将文本中的卡号给实体层，实体层传到DAL层进行查询。
                DataTable flag = facade.SelectStudent(stu);


                if (flag.Rows.Count != 0)//rows不等于0，说明存在cardno为控件内容的那么一行，所以已经存在。
                {
                    MessageBox.Show("用户已经存在", "温馨提示");
                    return;

                }
                else//将控件中的信息给实体层，后面再有的代码将实体层的信息给数据库。
                {
                    stu.cardno = txtCardno.Text.Trim();
                    stu.StudentName = txtName.Text.Trim();
                    stu.sex = comboBox1.Text.Trim();
                    stu.Ischeck = "未结账";
                    stu.studentNo = txtIdentity.Text.Trim();
                    stu.PWD = txtPwd.Text.Trim();
                    stu.cash =Convert.ToDouble( txtCharge.Text.Trim());
                    stu.UserID = txtLogoner.Text.Trim();
                    
                }
                DataTable flag1 = facade.AddStudent(stu);                
                MessageBox.Show("用户注册成功");

            }

        }

       
    }
}

Facade层

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;

namespace Facade
{
   public class StudentFacade
    {  
        //添加
        public DataTable AddStudent(Entity.Student_Info StudentInfo)
        {
            
            BLL.StudentBLL studentbll = new BLL.StudentBLL();//实例化一个BLL层
            DataTable result= studentbll.AddStudent(StudentInfo);
            return result;
        }        
    }
}

BLL层

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;

namespace BLL
{  
    public class StudentBLL
    {       
        //添加
        public DataTable AddStudent(Entity.Student_Info Student)
        {
            Factory.StudentFactory fact = new Factory.StudentFactory();
            IDAL.IStudentDAL idal = fact.Student();
            DataTable table = idal.AddStudent(Student);

            return table;
        }      
    }

}

Factory层

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Configuration;
using System.Reflection;

namespace Factory
{
    public class StudentFactory
    {
        string StrDB = ConfigurationManager.AppSettings["DB"];//需要引用命名空间Configuration；

        //打开StudentDAL层
        public IDAL.IStudentDAL Student()
        {
            string ClassName = StrDB + "." + "StudentDAL";//DAL.StudentDAL;
            return (IDAL.IStudentDAL)Assembly.Load(StrDB).CreateInstance(ClassName);
        }      
    }
}

IDAL层

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;

namespace IDAL
{
   public interface IStudentDAL
    {      
        DataTable AddStudent(Entity.Student_Info Student);//添加数据
    }
}

DAL层

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data;
using System.Data.SqlClient;
using Entity;
using System.Configuration;


namespace DAL
{
   public class StudentDAL:IDAL.IStudentDAL
    {
      

        public DataTable AddStudent(Entity.Student_Info Student)
        {
            SQLHelper sqlHelper = new SQLHelper();//实例化一个数据查询的对象。
            SqlParameter[] sqlParamsstu = { new SqlParameter("@cardno",Student.cardno ),
                                         new SqlParameter("@PWD", Student.PWD ),//SqlParameter是范围的意思，个人理解这行代码是规定新的东西。就是将PWD换成@password。
                                         
                               new SqlParameter("@StudentName",Student.StudentName),
                                         new SqlParameter("@sex",Student.sex),                                         
                                         new SqlParameter("@UserID",Student.UserID),
                                         new SqlParameter("@Ischeck",Student.Ischeck),                                         
                                         new SqlParameter("@cash",Student.cash),
                                   new SqlParameter("@studentNo",Student.studentNo)};
 
           string sqlstu = @"INSERT INTO Student_Info (cardno,PWD,StudentName,sex,UserID,Ischeck,cash,studentNo)
                        values(@cardno,@PWD,@StudentName,@sex,@UserID,@Ischeck,@cash,@studentNo)";//向数据库中插入新的数据。
           DataTable result = sqlHelper.ExecuteQuery1(sqlstu, sqlParamsstu, CommandType.Text);//SQLHelper查询，里面的参数依次是数据库插入、设置新参数、默认的枚举类型。
            return result;
        }

    }
}