账号密码管理系统Access版本

using System;
using System.Windows.Forms;
using System.Data.OleDb;
using System.Security.Cryptography;
using System.Text;

namespace 账号密码管理系统1._0
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        //登陆错误时调用此函数：错误次数加一
        private void IncErrortimes()
        {
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改。";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {
                    conn.Open();//打开连接

                    //创建数据库命令语句，更新错误次数加一
                    using (OleDbCommand UpdateCmd = conn.CreateCommand())
                    {
                        UpdateCmd.CommandText = "update T_system Set Errortimes=Errortimes+1 where sys_username=@name";
                        UpdateCmd.Parameters.Add(new OleDbParameter("name", textBox1.Text));
                        UpdateCmd.ExecuteNonQuery();

                    }
                }
            }
        }

        //登陆成功时调用此函数：重置错误次数
        private void ResetErrotimes()
        {
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改。";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {
                    conn.Open();//打开连接

                    //创建数据库命令语句
                    using (OleDbCommand UpdateCmd = conn.CreateCommand())
                    {
                        UpdateCmd.CommandText = "update T_system Set Errortimes=0 where sys_username=@name";
                        UpdateCmd.Parameters.Add(new OleDbParameter("name", textBox1.Text));
                        UpdateCmd.ExecuteNonQuery();

                    }
                }
            }
        }

        //秘钥清除使用
        private void RecoverErrotimes()
        {
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改。";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {
                    conn.Open();//打开连接

                    //创建SQL命令语句，重置错误次数为0
                    using (OleDbCommand UpdateCmd = conn.CreateCommand())
                    {
                        UpdateCmd.CommandText = "update T_system Set Errortimes=0 where sys_username=@name";
                        UpdateCmd.Parameters.Add(new OleDbParameter("name", textBox1.Text));
                        UpdateCmd.ExecuteNonQuery();

                    }

                    //创建SQL命令语句，恢复默认密码为root
                    using (OleDbCommand UpdateCmd = conn.CreateCommand())
                    {
                        UpdateCmd.CommandText = "update T_system Set sys_password=‘63a9f0ea7bb98050796b649e85481845‘ where sys_username=@name";
                        UpdateCmd.Parameters.Add(new OleDbParameter("name", textBox1.Text));
                        UpdateCmd.ExecuteNonQuery();

                    }
                }
            }
        }

        //当单击"登陆"按钮时执行以下事件处理程序
        private void button1_Click(object sender, EventArgs e)
        {
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改。";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {
                    conn.Open();//打开连接

                    //创建SQL命令语句
                    using (OleDbCommand cmd = conn.CreateCommand())
                    {
                        cmd.CommandText = "select * from T_system where sys_username=@name";
                        cmd.Parameters.Add(new OleDbParameter("name", GetMD5(textBox1.Text)));

                        //读取数据库查询结果进行用户名和密码判断
                        using (OleDbDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.Read())//用户名输入正确
                            {
                                int errortimes = reader.GetInt32(reader.GetOrdinal("Errortimes"));
                                if (errortimes > 3)
                                {

                                    if (textBox2.Text == "解锁 秘钥字符串，此处已经修改")
                                    {
                                        RecoverErrotimes();
                                        MessageBox.Show("程序解锁成功,程序即将重新启动！");
                                        Application.Exit();
                                        return;
                                    }
                                    else
                                    {
                                        MessageBox.Show("密码错误次数太多，程序已经被锁定禁用！");
                                        Application.Exit();
                                        return;

                                    }
                                }
                                string dbpassword = reader.GetString(reader.GetOrdinal("sys_password"));
                                if (dbpassword == GetMD5(textBox2.Text))//登陆成功！
                                {
                                    ResetErrotimes();//登陆成功，错误次数清零
                                    Form2 fm2 = new Form2();
                                    this.Hide();
                                    fm2.Show(); 
                                }
                                else
                                {
                                    MessageBox.Show("登陆失败！");
                                    IncErrortimes();
                                }
                            }
                            else   //用户输入错误
                            {
                                MessageBox.Show("用户名不存在！");

                            }
                        }
                    }
                }
            }
        }
        //MD5加密算法
        public static string GetMD5(string str)
        {
            MD5 md5 = MD5.Create();
            byte[] buffer = Encoding.Default.GetBytes(str);
            byte[] MD5buffer = md5.ComputeHash(buffer);
            string strnew = "";
            for (int i = 0; i < MD5buffer.Length; i++)
            {
                strnew += MD5buffer[i].ToString("x2");
            }
            return strnew;
        }
        //当单击"使用说明"文字标签时执行以下事件处理程序
        private void label4_Click(object sender, EventArgs e)
        {
            string information = "\t欢迎使用账号密码管理系统\n\n1.初始账号：root 密码: root \n\n2.登陆后请立即修改登陆账号和密码\n\n3.账号和密码打死也不能忘记和告诉其他人\n\n4.连续登陆错误次数多于4次，此程序将会被锁定禁用\n\n5.解锁需要用户和作者合作才能解锁成功！\n\n6.用户需提供用户名，作者提供清除错误次数秘钥,\n\n还原默认密码合作才能完成\n\n6.为了防止密码暴力破解以及系统锁定后无法使用，\n\n作者掌握清除错误次数和还原系统默认密码秘钥，但无法修改登陆账号\n\n因此如果登陆账号也忘记，作者也回天无力。\n\n7.联系作者：xingyun2684@gmail.com";
            MessageBox.Show(null, information, "使用说明：");

        }

        //当单击"重置"按钮时执行以下事件处理程序
        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = "";
            textBox2.Text = "";
        }
    }
}

using System;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Data.OleDb;
using System.Security.Cryptography;
using System.Text;
using System.IO;

namespace 账号密码管理系统1._0
{
    public partial class Form2 : Form
    {
        public Form2()
        {
            InitializeComponent();

            //combox1 下拉条内容初始化
            /**********************************************************/
           
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改。";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {
                    conn.Open();//打开连接

                    //创建SQL命令语句
                    using (OleDbCommand cmd = conn.CreateCommand())
                    {
                        //SQL查询语句
                        cmd.CommandText = "select account_type from T_users";
                        //读取查询结果内容
                        using (OleDbDataReader reader = cmd.ExecuteReader())
                        {
                            while (reader.Read())
                            {
                                comboBox1.Items.Add((reader.GetString(reader.GetOrdinal("account_type"))));
                            }
                        }
                    }
                }
            }
            /*********************************************************/
        }

        /*************************************************************************
               * 
               *               算法加密模块 
               * 
               * 登陆账号密码采用md5加密算法进行加密。
               * 
               * 信息内容采用 DES加密算法+MD5混合加密算法
               *  
               * 所有账号信息将调用此函数进行数据加密
               *
               *  调用方法：EncryptDES(string 明文字符串, string 秘钥字符串);
               *
               *            DecryptDES(string 密文字符串, string 秘钥字符串);
               *                                     
               * *********************************************************************/
       
        //DES普通加密解密算法
        
        // DES加密字符串
        private static byte[] Keys = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

        /************************************************************************
         *  
         * 解密函数：DecryptDES(string 密文字符串, string 秘钥字符串);
         * 
         * encryptString       待加密的字符串
         * 
         * encryptKey          加密密钥,要求为8位
         * 
         * 加密返回值        加密后的字符串，失败返回源串 
         * 
         * ***************************************************************************/
        public static string EncryptDES(string encryptString, string encryptKey)
        {
            try
            {
                byte[] rgbKey = Encoding.UTF8.GetBytes(encryptKey.Substring(0, 8));
                byte[] rgbIV = Keys;
                byte[] inputByteArray = Encoding.UTF8.GetBytes(encryptString);
                DESCryptoServiceProvider dCSP = new DESCryptoServiceProvider();
                MemoryStream mStream = new MemoryStream();
                CryptoStream cStream = new CryptoStream(mStream, dCSP.CreateEncryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
                cStream.Write(inputByteArray, 0, inputByteArray.Length);
                cStream.FlushFinalBlock();
                return Convert.ToBase64String(mStream.ToArray());
            }
            catch
            {
                return encryptString;
            }
        }

        /* *********************************************************************************/

        /* DES解密函数 DecryptDES(string 密文字符串, string 秘钥字符串);
         * 
         *        decryptString : 待解密的字符串
         * 
         *           decryptKey :   解密密钥,要求为8位,和加密密钥相同
         *        
         *                返回值:      解密成功返回解密后的字符串，失败返源串
         *
         ************************************************************************************/
        public static string DecryptDES(string decryptString, string decryptKey)
        {
            try
            {
                byte[] rgbKey = Encoding.UTF8.GetBytes(decryptKey);
                byte[] rgbIV = Keys;
                byte[] inputByteArray = Convert.FromBase64String(decryptString);
                DESCryptoServiceProvider DCSP = new DESCryptoServiceProvider();
                MemoryStream mStream = new MemoryStream();
                CryptoStream cStream = new CryptoStream(mStream, DCSP.CreateDecryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
                cStream.Write(inputByteArray, 0, inputByteArray.Length);
                cStream.FlushFinalBlock();
                return Encoding.UTF8.GetString(mStream.ToArray());
            }
            catch
            {
                return decryptString;
            }
        }
        //添加数据
/**************************************************************************/
        private void button1_Click(object sender, EventArgs e)
        {
           // 1. 判断是否数据库内已经有该条记录
        /*****************************************************************/
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改。";
            {
                    using (OleDbConnection conn2 = new OleDbConnection(connectionString)) 
                    {
                    conn2.Open();//打开连接

                    //创建SQL命令语句
                    using (OleDbCommand cmd = conn2.CreateCommand())
                    {
                        //SQL查询语句加密后查询
                        cmd.CommandText = "select account_type from T_users where account_type=‘" + textBox1.Text + "‘";
                        //读取查询结果内容
                        using (OleDbDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.Read())//如果存在
                            {
                                MessageBox.Show("对不起，同一类型的账号只能添加一次!", "添加失败提示");

                                //清空内容
                                textBox1.Text = "";
                                textBox2.Text = "";
                                textBox3.Text = "";
                                textBox4.Text = "";
                                textBox5.Text = "";
                                return;
                            }
                            else //数据库中不存在此类型账号则将其添加
                            {

                                //  更新combox 下拉选项 
                                comboBox1.Items.Add(textBox1.Text);
                                //添加信息插入到数据库内  
                                /***********************************************************************/
                                //与数据库建立连接
                                string connectionString2 = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
                                {
                                    using (OleDbConnection conn = new OleDbConnection(connectionString2))
                                    {
                                        conn.Open();//打开连接

                                        //创建SQL命令语句,添加内容都将会调用MD5算法进行加密，然后保存到数据库内。
                                        using (OleDbCommand insert_cmd = conn.CreateCommand())
                                        {
                                            //SQL查询语句
                                            insert_cmd.CommandText = "insert into T_users (account_type,account_website,account_username,account_password)values(‘" + textBox1.Text + "‘,‘" + EncryptDES(textBox2.Text, "信息md5加密字符串") + "‘,‘" + EncryptDES(textBox3.Text, "信息md5加密字符串") + "‘,‘" + EncryptDES(textBox4.Text, "信息md5加密字符串") + "‘);";
                                            insert_cmd.ExecuteNonQuery();
                                        }

                                    }
                                    /**************************************************/
                                    textBox1.Text = "";
                                    textBox2.Text = "";
                                    textBox3.Text = "";
                                    textBox4.Text = "";
                                    textBox5.Text = "";
                                    MessageBox.Show("插入成功！", "插入提示");
                                }
                            }
                        }
                    }
                }
            }
            }
        
/************************************************************************/

        //修改更新数据实现
/***********************************************************/
        private void button2_Click(object sender, EventArgs e)
        {
            //判断是否库中是否有此记录，有才可以修改。
            /************************************************************/
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {
                    conn.Open();//打开连接

                    //创建SQL命令语句
                    using (OleDbCommand cmd = conn.CreateCommand())
                    {
                        //SQL查询语句
                        cmd.CommandText = "select account_type from T_users where account_type=‘" + textBox1.Text + "‘;";
                        //读取查询结果内容
                        using (OleDbDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.Read())
                            {
                                //与数据库建立连接
                                string connectionString2 = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
                                {
                                    using (OleDbConnection conn2 = new OleDbConnection(connectionString2))
                                    {
                                        conn2.Open();//打开连接

                                        //创建SQL命令语句
                                        using (OleDbCommand modify_cmd = conn2.CreateCommand())
                                        {
                                            //SQL查询语句
                                            modify_cmd.CommandText = "update T_users set account_website=‘" + EncryptDES(textBox2.Text, "信息md5加密字符串") + "‘,account_username=‘" + EncryptDES(textBox3.Text, "信息md5加密字符串") + "‘,account_password=‘" + EncryptDES(textBox4.Text, "信息md5加密字符串") + "‘ where account_type=‘" + textBox1.Text + "‘;";
                                            modify_cmd.ExecuteNonQuery();

                                            //修改成功清空内容
                                            textBox1.Text = "";
                                            textBox2.Text = "";
                                            textBox3.Text = "";
                                            textBox4.Text = "";
                                            textBox5.Text = "";
                                            MessageBox.Show("修改成功！", "修改提示");
                                        }
                                    }
                                }
                            }
                            else
                            {
                                MessageBox.Show("数据库内没有该账号类型，无法修改！", "修改失败提示");
                                return;
                            }
                        }
                    }
                }
            }
        }

      /*********************************************************/
                
/***********************************************************/

        //删除数据实现
/********************************************************/
        private void button3_Click(object sender, EventArgs e)
        {
            /**********************************************************/
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {

                    conn.Open();//打开连接

                    //创建SQL命令语句
                    using (OleDbCommand cmd = conn.CreateCommand())
                    {
                        //SQL查询语句
                        cmd.CommandText = "select account_type from T_users where account_type=‘" + textBox1.Text + "‘;";
                        //读取查询结果内容
                        using (OleDbDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.Read())//存在该条记录
                            {
                                //执行删除操作
                                /*********************************************************/
                                //与数据库建立连接
                                string connectionString2 = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
                                {
                                    using (OleDbConnection conn2 = new OleDbConnection(connectionString2))
                                    {
                                        conn2.Open();//打开连接

                                        //创建SQL命令语句
                                        using (OleDbCommand delete_cmd = conn2.CreateCommand())
                                        {
                                            //SQL查询语句
                                            delete_cmd.CommandText = "delete from T_users where account_type=‘" + textBox1.Text+ "‘;";
                                            delete_cmd.ExecuteNonQuery();
                                        }
                                    }
                                }
                                //删除此combox选项
                                if (comboBox1.Text == textBox1.Text)
                                {
                                    comboBox1.Items.Remove(comboBox1.Text);
                                }
                                //删除成功清空内容
                                textBox1.Text = "";
                                textBox2.Text = "";
                                textBox3.Text = "";
                                textBox4.Text = "";
                                textBox5.Text = "";
                                MessageBox.Show("删除成功！", "删除成功提示");
                            }
                            else
                            {
                                MessageBox.Show("删除失败！", "删除失败提示");
                                return;
                            }
                        }
                    }
                }
            }
        }
/**************************************************************/

        //清空
/*************************************************************************/
        private void button6_Click(object sender, EventArgs e)
        {
            textBox1.Text = "";
            textBox2.Text = "";
            textBox3.Text = "";
            textBox4.Text = "";
            textBox5.Text = "";
        }
/*************************************************************************/
        
        //关键词搜索
        private void button4_Click(object sender, EventArgs e)
        {
            //与数据库建立连接
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {
                    conn.Open();//打开连接

                    //创建SQL命令语句
                    using (OleDbCommand cmd = conn.CreateCommand())
                    {
                        //SQL查询语句
                        cmd.CommandText = "select * from T_users where account_type=‘" + textBox5.Text + "‘;";

                        //读取查询结果内容
                        using (OleDbDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.Read())//账号类型存在存在
                            {
                                string db_type = reader.GetString(reader.GetOrdinal("account_type"));
                                string db_website = reader.GetString(reader.GetOrdinal("account_website"));
                                string db_username = reader.GetString(reader.GetOrdinal("account_username"));
                                string db_password = reader.GetString(reader.GetOrdinal("account_password"));
                                textBox1.Text =db_type;
                                textBox2.Text = DecryptDES(db_website, "信息md5加密字符串");
                                textBox3.Text = DecryptDES(db_username, "信息md5加密字符串");
                                textBox4.Text = DecryptDES(db_password, "信息md5加密字符串");
                            }
                            else //reader返回false，搜索没有找到
                            {
                                MessageBox.Show("对不起，没有找到！", "搜索提示");
                                return;
                            }
                        }
                    }
                }
            }

        }
        
        //下拉框搜索
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
            {
                using (OleDbConnection conn = new OleDbConnection(connectionString))
                {
                    conn.Open();//打开连接

                    //创建SQL命令语句
                    using (OleDbCommand cmd = conn.CreateCommand())
                    {
                        //SQL查询语句
                        cmd.CommandText = "select * from T_users where account_type=‘" + comboBox1.Text +"‘";
                        //读取查询结果内容
                        using (OleDbDataReader reader = cmd.ExecuteReader())
                        {
                            if (reader.Read())
                            {
                                textBox1.Text =reader.GetString(reader.GetOrdinal("account_type"));
                                textBox2.Text = DecryptDES((reader.GetString(reader.GetOrdinal("account_website"))), "信息md5加密字符串");
                                textBox3.Text = DecryptDES((reader.GetString(reader.GetOrdinal("account_username"))), "信息md5加密字符串");
                                textBox4.Text = DecryptDES((reader.GetString(reader.GetOrdinal("account_password"))), "信息md5加密字符串");
                            }
                            else
                            {
                                comboBox1.Items.Remove(comboBox1.Text);
                                return;
                            }
                        }
                    }
                }
            }
        }

        
        /* 在winform中，系统默认是不能够禁用窗体的关闭功能，
         * 但是，有时我们需要这种功能来屏蔽用户"随便"或不小心关闭造成的系统问题。 
         * 该方法操作起来十分简便，只要将以下一段代码添加到窗体累中就可以实现禁止窗体关闭按钮
         * 该方法让窗体的关闭按钮还是存在的，但是，鼠标操作关闭按钮是没有效果的。
         */
    /****************************************************************************/
        //禁用鼠标右上角关闭按钮
        protected override void WndProc(ref   Message m)
        {
            const int WM_SYSCOMMAND = 0x0112;
            const int SC_CLOSE = 0xF060;
            if (m.Msg == WM_SYSCOMMAND && (int)m.WParam == SC_CLOSE)
            {
                return;
            }
            base.WndProc(ref m);
        }
   /***********************************************************************/

        //系统维护
        private void button5_Click(object sender, EventArgs e)
        {
            Form3 fm3 = new Form3();
            this.Hide();
            fm3.Show();
        }

        //退出系统
        private void button7_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }
    }
}

using System;
using System.Windows.Forms;
using System.Data.SqlClient;
using System.Data.OleDb;
using System.Security.Cryptography;
using System.Text;

namespace 账号密码管理系统1._0
{
    public partial class Form3 : Form
    {
        public Form3()
        {
            InitializeComponent();
        }

        //重置
        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Text = "";
            textBox2.Text = "";
            textBox3.Text = "";
            textBox4.Text = "";
            textBox5.Text = "";
        }

        //修改
        private void button1_Click(object sender, EventArgs e)
        {
            if (textBox4.Text == textBox5.Text)
            {
                //与数据库建立连接
                string connectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
                {
                    using (OleDbConnection conn = new OleDbConnection(connectionString))
                    {
                        conn.Open();//打开连接

                        //创建SQL命令语句
                        using (OleDbCommand cmd = conn.CreateCommand())
                        {
                            //SQL查询语句
                            cmd.CommandText = "select * from T_system where sys_username=‘" + GetMD5(textBox1.Text) + "‘;";
                            //读取查询结果内容
                            using (OleDbDataReader reader = cmd.ExecuteReader())
                            {
                                if (reader.Read())//判断用户名是否存在
                                {
                                    string dbpassword = reader.GetString(reader.GetOrdinal("sys_password"));
                                    if (dbpassword == GetMD5(textBox2.Text)) //原来密码输入正确
                                    {
                                        //更新数据库
                                        //添加信息插入到数据库内  
                                        /***********************************************************************/
                                        //与数据库建立连接
                                        string connectionString2 = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=Account_System.mdb;Jet OLEDB:Database Password=数据库密码设置处,此处已经修改";
                                        {
                                            using (OleDbConnection conn2 = new OleDbConnection(connectionString2))
                                            {
                                                conn2.Open();//打开连接

                                                //创建SQL命令语句
                                                using (OleDbCommand insert_cmd = conn2.CreateCommand())
                                                {
                                                    //SQL查询语句
                                                    insert_cmd.CommandText = "update T_system set sys_username=‘" + GetMD5(textBox3.Text) + "‘,sys_password=‘" + GetMD5(textBox4.Text) + "‘;";
                                                    insert_cmd.ExecuteNonQuery();
                                                }
                                            }
                                        }
                                        MessageBox.Show("恭喜您，修改成功！", "系统维护提示");

                                    }
                                    else//原密码输入错误 
                                    {
                                        MessageBox.Show("对不起，原密码输入错误");
                                        return;
                                    }
                                }
                                else
                                {
                                    MessageBox.Show("原用户名输入错误！");
                                    return;
                                }
                            }
                        }

                    }
                }
            }
            else
            {
                MessageBox.Show("修改失败，新密码与确认密码不一致！", "修改错误提示");
                return;
            }

        }
        //MD5加密算法
        public static string GetMD5(string str)
        {
            MD5 md5 = MD5.Create();
            byte[] buffer = Encoding.Default.GetBytes(str);
            byte[] MD5buffer = md5.ComputeHash(buffer);
            string strnew = "";
            for (int i = 0; i < MD5buffer.Length; i++)
            {
                strnew += MD5buffer[i].ToString("x2");
            }
            return strnew;
        }

        private void button3_Click(object sender, EventArgs e)
        {
            Form2 fm2 = new Form2();
            this.Hide();
            fm2.Show();  
        }
    }
}