void edit() {

    system("cls");
    cout << "Enter the number of the student you want to change: ";
    int num;

    cin >> num;
    num = num - 1;

    ifstream fin("Show.txt", ios::in);
    n = 0;
    while (!fin.eof()) {
        fin >> spisok[n].name;
        if (spisok[n].name == "") break;
        fin >> spisok[n].surname;
        fin >> spisok[n].patronymic;
        fin >> spisok[n].number_group;
        fin >> spisok[n].birthYear;
        fin >> spisok[n].physics;
        fin >> spisok[n].math;
        fin >> spisok[n].informatics;
        fin >> spisok[n].chemistry;
        fin >> spisok[n].gap;
        n++;
    }
    cout << "Choose what you want to change: " << endl;

    cout << "1. Name." << endl;
    cout << "2. Surname." << endl;
    cout << "3. Thirdname." << endl;
    cout << "4. Number of group." << endl;
    cout << "5. Date of birth." << endl;
    cout << "6. Physics." << endl;
    cout << "7. Mathematics" << endl;
    cout << "8. Informatics" << endl;
    cout << "9. Chemistry" << endl;


    int kl = 0;
    cin >> kl;
    system("cls");

    if (kl == 1) {
        cout << "Enter new name: ";
        string name;
        cin >> name;
        spisok[num].name = name;
    }
    else
        if (kl == 2) {
            cout << "Enter new surname: ";
            string nam;
            cin >> nam;
            spisok[num].surname = nam;
        }
        else
            if (kl == 3) {
                cout << "Enter new patronymic: ";
                string nam;
                cin >> nam;
                spisok[num].patronymic = nam;
            }
            else
                if (kl == 4) {
                    cout << "Enter new number of group: ";
                    int nam;
                    cin >> nam;
                    spisok[num].number_group = nam;
                }
                else
                    if (kl == 5) {
                        cout << "Enter new date of birth: ";
                        int nam;
                        cin >> nam;
                        spisok[num].birthYear = nam;
                    }
                    else
                        if (kl == 6) {
                            cout << "Enter new a physics grade: ";
                            int nam;
                            cin >> nam;
                            spisok[num].physics = nam;
                        }
                        else
                            if (kl == 7) {
                                cout << "Enter new a math grade: ";
                                int nam;
                                cin >> nam;
                                spisok[num].math = nam;
                            }
                            else
                                if (kl == 8) {
                                    cout << "Enter new an informatics grade: ";
                                    int nam;
                                    cin >> nam;
                                    spisok[num].informatics = nam;
                                }
                                else
                                    if (kl == 9) {
                                        cout << "Enter new a chemistry grade: ";
                                        int nam;
                                        cin >> nam;
                                        spisok[num].chemistry = nam;
                                    }

    ofstream fout("Show.txt", ios::out);

    for (int i = 0; i < n; i++) {
        fout << spisok[i].name << " ";
        fout << spisok[i].surname << " ";
        fout << spisok[i].patronymic << " ";
        fout << spisok[i].number_group << " ";
        fout << spisok[i].birthYear << " ";
        fout << spisok[i].physics << " ";
        fout << spisok[i].math << " ";
        fout << spisok[i].informatics << " ";
        fout << spisok[i].chemistry << " ";
        fout << spisok[i].gap << endl;
    }
    system("cls");

    cout << "Changes have been made." << endl;
}