private void Button_Click(object sender, RoutedEventArgs e)
        {
            int i = 0;

            foreach (StudentDataUserControl item in students.Children)
            {
                Evaluator.StudentsAnswersWithErrors[i].Student.RegNo     = Int32.Parse(item.regNo.Text);
                Evaluator.StudentsAnswersWithErrors[i].Student.FirstName = item.firstName.Text;
                Evaluator.StudentsAnswersWithErrors[i].Student.LastName  = item.lastName.Text;
                Evaluator.StudentsAnswersWithErrors[i].Group.Name        = item.group.Text;
                i++;
            }
            Evaluator.FixingErrors();

            IsNonCloseButtonClicked = true;
            this.Close();
        }