private void LoginCheck()
        {
            bool   success = false;
            string line;
            bool   admin = false;

            StreamReader file = new StreamReader("users.txt");

            while ((line = file.ReadLine()) != null)
            {
                string[] podaci = line.Split(',');
                if ((username == podaci[0]) && (password == podaci[1]))
                {
                    if (podaci[2] == "admin")
                    {
                        admin = true;
                    }
                    MessageBox.Show("Uspesan login!");
                    success = true;
                    id      = int.Parse(podaci[8]);
                }
            }
            file.Close();
            if (success)
            {
                if (admin)
                {
                    k = new Administrator(username, password);
                    Form frm = new AdministratorForm();
                    frm.Show();
                    this.Hide();
                    //Otvara se forma za administratora.
                }

                else
                {
                    k = new Kupac(username, password);
                    UserForm frm = new UserForm();
                    frm.LoadUsernamePassword(username, password, id);
                    frm.Show();
                    this.Hide();
                    //Otvara se forma za korisnika.
                }
            }
            else
            {
                MessageBox.Show("Neuspesan login. Pokusajte ponovo.");
            } textBox1.Clear(); textBox2.Clear();
        }
        private void CheckLogin()
        {
            bool         success = false;
            string       line;
            bool         admin = false;
            StreamReader file  = new StreamReader("users.txt");

            while ((line = file.ReadLine()) != null)
            {
                string[] podaci = line.Split(',');
                if ((username == podaci[0]) && (password == podaci[1]))
                {
                    if (podaci[2].Equals("admin"))
                    {
                        admin = true;
                        MessageBox.Show("Admin");
                    }
                    MessageBox.Show("Uspesno");
                    success = true;
                }
            }
            file.Close();
            if (success)
            {
                if (admin)
                {
                    k = new Administrator(username, password);
                    Form frm = new AdministratorForm();
                    frm.Show();
                    this.Hide();
                    //FORMA ADMIN
                }
            }
            else
            {
                MessageBox.Show(username, password);
                k = new Kupac(username, password);
                Form frm = new UserForm();
                frm.Show();
                this.Hide();
                //FORMA KORISNIK
            }
        }