Lập trình C# - Code đăng nhập

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Text;using System.Windows.Forms;using System.IO;
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Lập trình C# - Code đăng nhậpusing System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Text;using System.Windows.Forms;using System.IO;namespace BAIBACCAO{ public partial class notepad : Form { public notepad() { InitializeComponent(); } String filename = ; private void deleteToolStripMenuItem_Click(object sender,EventArgs e) { txtnoidung.Clear(); } private void newToolStripMenuItem_Click(object sender, EventArgse) { txtnoidung.Text = ; this.Text = Untitled; filename = ; } private void openToolStripMenuItem_Click(object sender,EventArgs e) { openFileDialog1.Filter = Text Files (*.txt)|*.txt|WordDocuments + (*.doc)|*.doc|All Files (*.*)|*.*; try { if (openFileDialog1.ShowDialog() == DialogResult.OK) { filename = openFileDialog1.FileName; this.Text = filename; StreamReader strReader;// bien dung de doc du lieura strReader = File.OpenText(filename); txtnoidung.Text = strReader.ReadToEnd(); strReader.Close(); } } catch { MessageBox.Show(Lỗi chương trình ?); } } private void saveToolStripMenuItem_Click(object sender,EventArgs e) { if (filename == ) { saveFileDialog1.Filter = Text Files (*.txt)|*.txt|WordDocuments + (*.doc)|*.doc|All Files (*.*)|*.*; saveFileDialog1.FileName = Untitled; if (saveFileDialog1.ShowDialog() == DialogResult.OK) { //Luu noi dung filename = saveFileDialog1.FileName; FileStream fStream;//chua ten moi StreamWriter strWriter;//dung doc fStream = File.Create(filename); fStream.Close(); strWriter = File.AppendText(filename); strWriter.Write(txtnoidung.Text); strWriter.Close(); this.Text = filename; } } else { //Luu noi dung FileStream fStream; StreamWriter strWriter; fStream = File.Create(filename); fStream.Close(); strWriter = File.AppendText(filename); strWriter.Write(txtnoidung.Text); strWriter.Close(); this.Text = filename; } } private void saveAsToolStripMenuItem_Click(object sender,EventArgs e) { saveFileDialog1.Filter = Text Files (*.txt)|*.txt|WordDocuments + (*.doc)|*.doc|All Files (*.*)|*.*; saveFileDialog1.FileName = Untitled; if (saveFileDialog1.ShowDialog() == DialogResult.OK) { filename = saveFileDialog1.FileName; FileStream fStream; //bien chua ten file can tao deluu StreamWriter strWriter; //bien dung de ghi du lieuvao fStream = File.Create(filename); fStream.Close(); //tao song roi dong lai strWriter = File.AppendText(filename); //gan noi dungvao cho bien strWriter.Write(txtnoidung.Text); //thuc hien ghi strWriter.Close(); } } private void exitToolStripMenuItem_Click(object sender,EventArgs e) { Close(); } private void notepad_Load(object sender, EventArgs e) { txtnoidung.Size = new Size(this.ClientRectangle.Width - 4,this.ClientRectangle.Height - 28); txtnoidung.Location = new Point(2, 26); } private void notepad_Resize(object sender, EventArgs e) { txtnoidung.Size = new Size(this.ClientRectangle.Width - 4,this.ClientRectangle.Height - 28); txtnoidung.Location = new Point(2, 26); } private void unduToolStripMenuItem_Click(object sender,EventArgs e) { txtnoidung.Undo(); } private void cutToolStripMenuItem_Click(object sender, EventArgse) { txtnoidung.Cut(); } private void pastToolStripMenuItem_Click(object sender,EventArgs e) { txtnoidung.Paste(); } private void copyToolStripMenuItem_Click(object sender,EventArgs e) { txtnoidung.Copy(); } private void selectAllToolStripMenuItem_Click(object sender,EventArgs e) { txtnoidung.SelectAll(); } private void dataTimeToolStripMenuItem_Click(object sender,EventArgs e) { System.DateTime currentTime = System.DateTime.Now; txtnoidung.Text = txtnoidung.Text + + DateTime.Now; } private void fontToolStripMenuItem_Click(object sender,EventArgs e) { if (fontDialog1.ShowDialog() == DialogResult.OK) { txtnoidung.Font = fontDialog1.Font; } } private void fontcolorToolStripMenuItem_Click(object sender,EventArgs e) { if (colorDialog1.ShowDialog() == DialogResult.OK) { txtnoidung.ForeColor = colorDialog1.Color; } } private void backGoundToolStripMenuItem_Click(object sender,EventArgs e) { if (c ...