//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 = http://www.mamicode.com/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();        }    }