C#_连接数据库实现 登录注册界面

//编写登录界面逻辑
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.SqlClient;

namespace LoginDatabase
{
    public partial class Login : Form
    {
        private int errorTime = 3;

        public Login() {
            InitializeComponent();
        }

        private void loginBtn_Click(object sender, EventArgs e) {
            errorTime = errorTime - 1;

            string username = txtName.Text.Trim();  //取出账号
            string pw = txtPwd.Text.Trim();         //取出密码
            string constr = "Server=.;DataBase=SU; Integrated Security=True"; //设置连接字符串
            SqlConnection mycon = new SqlConnection(constr);  //实例化连接对象
            mycon.Open();

            SqlCommand mycom = mycon.CreateCommand();         //创建SQL命令执行对象
            string s1 = "select account,password from register where account='" + username + "' and password='" + pw + "'";                                            //编写SQL命令
            mycom.CommandText = s1;                           //执行SQL命令
            SqlDataAdapter myDA = new SqlDataAdapter();       //实例化数据适配器
            myDA.SelectCommand = mycom;                       //让适配器执行SELECT命令
            DataSet myDS = new DataSet();                     //实例化结果数据集
            int n = myDA.Fill(myDS, "register");              //将结果放入数据适配器，返回元祖个数
            if (n != 0) {
                if (checkCode.Text == textCheck.Text) { 
                    MessageBox.Show("欢迎使用！");             //登录成功
                    this.Close();
                } else {
                    MessageBox.Show("验证码填写错误");
                    textCheck.Text = "";
                }
            } else
                if (errorTime < 3) {
                    MessageBox.Show("用户名或密码有错。请重新输入！还有" + errorTime.ToString() + "次机会");
                    txtName.Text = "";   //清空账号
                    txtPwd.Text = "";    //清空密码?
                    txtName.Focus();     //光标设置在账号上
                } else {
                    MessageBox.Show("你输入的用户名或密码已达三次? 将退出程序");
                    this.Close();
                }

        }

        private void cancelBtn_Click(object sender, EventArgs e) {
            Application.Exit();
        }

        private void button1_Click(object sender, EventArgs e) {
            Register register = new Register();
            register.ShowDialog();
        }

        private void checkCode_Click(object sender, EventArgs e) {
            Random random = new Random();
            int minV = 12345, maxV = 98765;
            checkCode.Text = random.Next(minV, maxV).ToString();
        }
    }
}

5.编写注册界面逻辑
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace LoginDatabase
{
    public partial class Register : Form
    {
        public Register() {
            InitializeComponent();
        }

        private void btnRegister_Click(object sender, EventArgs e) {

            //检查是否已经存在
            string userID = userId.Text.Trim();  //取出账号
            
            /**
             * 连接数据库
             */ 
            string constr = "Server=.;DataBase=SU; Integrated Security=True"; //设置连接字符串
            SqlConnection mycon = new SqlConnection(constr);                  //实例化连接对象
            mycon.Open();


            //查询新注册的用户是否存在
            SqlCommand checkCmd = mycon.CreateCommand();       //创建SQL命令执行对象
            string s = "select account from register where account='" + userID + "'";
            checkCmd.CommandText = s;
            SqlDataAdapter check = new SqlDataAdapter();       //实例化数据适配器
            check.SelectCommand = checkCmd;                    //让适配器执行SELECT命令
            DataSet checkData = new DataSet();                 //实例化结果数据集
            int n = check.Fill(checkData, "register");         //将结果放入数据适配器，返回元祖个数
            if (n != 0) {
                MessageBox.Show("用户名存在");
                userId.Text = ""; userPw.Text = "";
                nickName.Text = "";
            }
     

            //确认密码
            if (ensurePw.Text != userPw.Text) {
                ensurePw.Text = "";
            }

            //验证码
            if (textCheck.Text != checkCode.Text) {
                textCheck.Text = "";
            }

            //插入数据SQL  逻辑
            string s1 = "insert into Register(account,password,nickname) values ('" + userId.Text + "','" + userPw.Text + "','"
                + nickName.Text + "')";                            //编写SQL命令
            SqlCommand mycom = new SqlCommand(s1, mycon);          //初始化命令
            mycom.ExecuteNonQuery();             //执行语句
            mycon.Close();                       //关闭连接
            mycom = null;
            mycon.Dispose();                     //释放对象


            if (userId.Text == "" || userPw.TextLength <= 6 || nickName.Text == "" || ensurePw.Text == ""
                || textCheck.Text == "") {
                MessageBox.Show("请将信息填完整");
            } else {
                MessageBox.Show("注册成功");
                this.Close();
            }
        }

        private void checkCode_Click(object sender, EventArgs e) {
            Random random = new Random();
            int minV = 12345, maxV = 98765;
            checkCode.Text = random.Next(minV, maxV).ToString();
        }
    }