public Form1()
{
 InitializeComponent();
 //登录按钮
 button1.Click += delegate
 {
  this.DialogResult = DialogResult.OK;
  this.Close();
 };
 //取消登录按钮
 button2.Click += delegate
 {
  this.DialogResult = DialogResult.Cancel;
 };
 //窗体关闭
 this.FormClosing += delegate(object sender, FormClosingEventArgs e)
 {
  if (this.DialogResult != DialogResult.Cancel && this.DialogResult != DialogResult.OK)
   e.Cancel = true;
 };
}

[STAThread]
tatic void Main(string[] args)
{
 if (args.Length > 0)
  MessageBox.Show(args[0]);
 Application.EnableVisualStyles();
 Application.SetCompatibleTextRenderingDefault(false);
  FrmLogin f = new FrmLogin ();
 if (f.ShowDialog() == DialogResult.OK)
 {
  Application.Run(new Form3());
 }
}