private void btnRegister_Click(object sender, EventArgs e)
        {
            User user = new User()
            {
                Name     = this.txbRegisterName.Text,
                Surname  = this.txbRegisterSurname.Text,
                Email    = this.txbRegisterEmail.Text,
                Password = this.txbRegisterPassword.Text,
                Phone    = this.txbRegisterPhone.Text,
                Type     = (int)UserTypeEnum.User,
            };
            bool isValid = ValidationOperation <User> .ValidateOperation(user);

            bool IsUnique = EmailValidation.IsUniqueEmail(user);

            if (IsUnique)
            {
                if (isValid)
                {
                    UserDAL userDAL = new UserDAL();
                    userDAL.Add(user);
                    MessageBox.Show("Successfully Registered!");
                    this.Close();
                }
            }
            else
            {
                MessageBox.Show("The email is already used.");
            }
        }