namespace WinForm
{
    static class Program
    {
        /// <summary>
        ///  The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.SetHighDpiMode(HighDpiMode.SystemAware);
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}

        private void Form1_Load(object sender, EventArgs e)
        {
            Login login = new Login();
            login.ShowDialog();
            string a = "123";
            MessageBox.Show(a + "用户登录成功");
        }

private void button1_Click(object sender, EventArgs e)
        {
            if (textBox1.Text.Equals("123"))
            {
                this.Dispose();
            }
            else {
                MessageBox.Show("错误");
                return;
            }
        }