static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            FormLogin log = new FormLogin();
            Application.Run(log);

            if (log.login)
                Application.Run(new FormPrincipal());
        }
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            FormLogin log = new FormLogin();

            Application.Run(log);

            if (log.login)
            {
                Application.Run(new FormPrincipal());
            }
        }