Добавление элемента в динамическую структуру

#include<iostream>
#include<string>
#include<cstring>
#include<cstdlib>
#include<fstream>
#include<string>
#include<iomanip>
 
using namespace std;
char filename[] = "info.txt";
bool k = false;
 
struct student {
    string name;
    string secondname;
    string thirdname;
    int age;
    int course;
    double yspevaemost;
};
double sredniyball(student *a, int n, int k);
int cout_student_with_low_marks(student *a, int n, double sredniy, int k);
int menu_change();
void add_student(student *studentx, int number_student);
void read_file(student *studentx, int &number_student);
void vivod_info(student *studentx, int &number_student);
void save_in_file(student *studentx, int &number_student);
int kol_vo_students();
void myCopy(student* to, const student* from, int count);
 
int main() {
    setlocale(LC_ALL, "Russian");
    int number_student = kol_vo_students();
    student *studentx = new student[number_student];
    read_file(studentx, number_student);
    vivod_info(studentx, number_student);
    //add_student(studentx, number_student);
    //vivod_info(studentx, number_student);
    vivod_info(studentx, number_student);
    system("pause");
    return 0;
}
void myCopy(student* to, const student* from, int count)
{
    while (count--) {
        *to = *from;
        ++to;
        ++from;
    }
}
double sredniyball(student *a, int n, int k) {
    double sum = 0;
    for (int i = 0; i < n; i++) {
        if (a[i].course == k) { sum += a[i].yspevaemost; }
    }
    return sum / n;
}
 
int cout_student_with_low_marks(student *a, int n, double sredniy, int k) {
    int kolvo = 0;
    for (int i = 0; i < n; i++) {
        if (a[i].yspevaemost < sredniy&&a[i].course == k) {
            kolvo++;
        }
    }
    return kolvo;
}
int menu_change()
{
    int variant;
    cout << "************************\n"
        << "*What u want to change?*\n" << endl;
    cout << "*1. Prosmotr soderjimogo *\n"
        << "*2. Add                *\n"
        << "*3. dell              *\n"
        << "*4. change              *\n"
        << "*5. individual'noe             *\n"
        << "*6. quit               *`\n"
        << "**************************\n";
    cout << ">>> ";
    cin >> variant;
    return variant;
}
 
void read_file(student *studentx, int &number_student) {
    ifstream f(filename);
    char temp[500];
    number_student = 0;
    while (!f.eof()) {
        f >> temp;
        studentx[number_student].name = temp;
        f >> temp;
        studentx[number_student].secondname = temp;
        f >> temp;
        studentx[number_student].thirdname = temp;
        f >> temp;
        studentx[number_student].age = atoi(temp);
        f >> temp;
        studentx[number_student].course = atoi(temp);
        f.getline(temp, 500);
        studentx[number_student].yspevaemost = atof(temp);
        number_student++;
    }
    f.close();
}
void add_student(student *studentx, int number_student) {
    //number_student--;
    cout << "Write Name: "; cin >> studentx[number_student].name;
        cout << "WRite secondname:"; cin >> studentx[number_student].secondname;
        cout << "Write thirdname: "; cin >> studentx[number_student].thirdname;
        cout << "Write age: "; cin >> studentx[number_student].age;
        cout << "Write course: "; cin >> studentx[number_student].course;
        cout << "Write yspevaemost'"; cin >> studentx[number_student].yspevaemost;
        save_in_file(studentx, number_student);
    //number_student++;
}
 
void vivod_info(student *studentx, int &number_student) {
    cout << "ID# " << setw(8) << left << "Name"
        << setw(11) << "Secondname "
        << setw(15) << "Thirdname"
        << setw(5) << "Age"
        << setw(7) << "сourse"
        << setw(12) << "Academic performance"
        << std::endl;
    for (int i = 0; i < number_student; i++) {
        cout << i + 1 << "   " << setw(8) << left << studentx[i].name
            << setw(11) << studentx[i].secondname
            << setw(15) << studentx[i].thirdname
            << setw(5) << studentx[i].age
            << setw(7) << studentx[i].course
            << setw(12) << studentx[i].yspevaemost
            << std::endl;
    }
}
void save_in_file(student *studentx, int &number_student) {
    ofstream g(filename);
    for (int i = 0; i < number_student; i++) {
        g << studentx[i].name << " "
            << studentx[i].secondname << " "
            << studentx[i].thirdname << " "
            << studentx[i].age << " "
            << studentx[i].course << " "
            << studentx[i].yspevaemost << endl;
    }
    g.close();
}
int kol_vo_students() {
    int kol_vo=0;
    char temp[500];
    ifstream f(filename);
    while (!f.eof()) {
        f.getline(temp,500);
        kol_vo++;
    }
    f.close();
    return kol_vo;
}

#include <iostream>
#include <cstring>
 
int main()
{
    int size{ 5 };
    int *arr = new int[size]{ 1, 2, 3, 4, 5 };
    // Вывод
    for (int i{}; i < size; ++i)
    {
        std::cout << arr[i] << ' ';
    }
    std::cout << std::endl;
    // Нужно добавить элемент - памяти не хватает. Перевыделим память.
    {
        int new_size{ size * 2 };
        int *new_arr = new int[new_size];
        std::memmove(new_arr, arr, sizeof(int) * size); // копируем элементы из arr в новый массив
        delete[] arr; // освободим память из под уже СТАРОГО массива
        arr = new_arr; // и установим указатель на новый
        size = new_size; // сохраним новый размер
    }
    // Добавим элементов
    arr[5] = 5;
    arr[6] = 4;
    arr[7] = 3;
    arr[8] = 2;
    arr[9] = 1;
    // Вывод
    for (int i{}; i < size; ++i)
    {
        std::cout << arr[i] << ' ';
    }
    std::cout << std::endl;
    
    delete[] arr;
}