Создать запись для хранения следующей информации:

#include "pch.h"
#include <iostream>
#include <string>
 
using namespace std;
 
struct DATE
{
    int number;
    int month;
    int year;
};
typedef struct informations
{
    char code[10];//код владельца
    char number_car[10];//номер автомобиля
    char mark[10];//марка автомобиля
    DATE release;//дата выпуска
    DATE registration;//дата регистрации
    struct informations* next;
 
} Informations;
 
Informations* top = NULL;         //??? Почему NULL
 
void push() //ввод
{
    Informations* ptr= (Informations *)malloc(sizeof(Informations));   //??? Зачем здесь malloc
 
    cin.get();
    cout << "Enter the code owner: ";
    cin.getline(ptr->code, 9);
    cout << "Enter the number of the car: ";
    cin.getline(ptr->number_car, 9);
    cout << "Enter the mark of the car: ";
    cin.getline(ptr->mark, 9);
 
    cout << "Enter the date of release: " << endl;
    do {
        cout << "number: ";
        cin >> ptr->release.number;
    } while ((ptr->release.number > 31) || (ptr->release.number <= 0));   //??? Почему в этой и последующих строках условие (>31 и <=0) , а не наоборот
    do {
        cout << "month: ";
        cin >> ptr->release.month;
    } while ((ptr->release.month > 12) || (ptr->release.month <= 0));
    do {
        cout << "year: ";
        cin >> ptr->release.year;
    } while (ptr->release.year < 0);
 
    cout << "Enter the date of registration: " << endl;
    do {
        cout << "number: ";
        cin >> ptr->registration.number;
    } while ((ptr->registration.number > 31) || (ptr->registration.number <= 0));
    do {
        cout << "month: ";
        cin >> ptr->registration.month;
    } while ((ptr->registration.month > 12) || (ptr->registration.month <= 0));
    do {
        cout << "year: ";
        cin >> ptr->registration.year;
    } while (ptr->registration.year < 0);
    cout << endl;
 
    ptr->next = top;     //??? Что это за приравнивание в этой и следующей строке 
    top = ptr;
}
void pop() //удаление.   //??? Как сделать удаление одной записи, а не всех
{
    while (top != NULL)
        //for ( int i=0;   ; i++)
    {
        Informations* ptr = top->next;
        //if (i==p)
        //{
        cout << top->code << "  ";
        cout << top->number_car << "  ";
        cout << top->mark << " - deleted\n";
        free(top);
        top = ptr;
        //ptr = top->next;
        //break;
    //}
    }
}
void show_stack() //просмотр элем стека
{
    int i = 0;
    cout << endl;
    Informations* ptr = top;
    while (ptr != NULL)
    {
        i++;
        cout << "           " << i << endl;
        cout << "The code owner: " << ptr->code << endl;
        cout << "The number of the car: " << ptr->number_car << endl;
        cout << "The mark of the car: " << ptr->mark << endl;
        cout << "The date of release:\nnumber: " << ptr->release.number
            << "\nmonth: " << ptr->release.month
            << "\nyear: " << ptr->release.year << "\n\n";
        cout << "The date of registration:\nnumber: " << ptr->registration.number
            << "\nmonth: " << ptr->registration.month
            << "\nyear: " << ptr->registration.year << "\n\n";
        ptr = ptr->next;
    }
}
void change()//изменение
{
    //Informations* ptr = top->next;
    cin.get();
    cout << "Enter the code owner: ";
    cin.getline(top->code, 9);
    cout << "Enter the number of the car: ";
    cin.getline(top->number_car, 9);
    cout << "Enter the mark of the car: ";
    cin.getline(top->mark, 9);
 
    cout << "Enter the date of release:" << endl;
    do {
        cout << "number: ";
        cin >> top->release.number;
    } while ((top->release.number > 31) || (top->release.number <= 0));
    do {
        cout << "month: ";
        cin >> top->release.month;
    } while ((top->release.month > 12) || (top->release.month <= 0));
    do {
        cout << "year: ";
        cin >> top->release.year;
    } while (top->release.year < 0);
 
    cout << "Enter the date of registration: " << endl;
    do {
        cout << "number: ";
        cin >> top->registration.number;
    } while ((top->registration.number > 31) || (top->registration.number <= 0));
    do {
        cout << "month: ";
        cin >> top->registration.month;
    } while ((top->registration.month > 12) || (top->registration.month <= 0));
    do {
        cout << "year: ";
        cin >> top->registration.year;
    } while (top->registration.year < 0);
    cout << endl;
}
void November_and_December()
{
    Informations* ptr = top;
    while (ptr != NULL)
    {
        if ((ptr->registration.month == 11) || (ptr->registration.month == 12));
        cout << "The number of the car: " << ptr->number_car << endl;
        cout << "The mark of the car: " << ptr->mark << endl;
        ptr = ptr->next;
    }
}
void Average_age()
{
    ;
}
void main()
{
    int l;
    do
    {
        cout << "--------------------------------------";
        cout << endl;
        cout << " 1)Enter " << endl << " 2)Show " << endl << " 3)Search " << endl << " 4)Delete " << endl << " 5)Change " << endl << " 6)November and December" << endl << " 7)Average age" << endl << " 8)Exit " << endl;
        cin >> l;
        switch (l)
        {
        case 1:push(); break;
        case 2:show_stack(); break;
        case 4:
        {
            //int p;
            //cin>>p;
            if (top != NULL) pop(); break;
        }
        case 5:
        {
            //int p;
            //cin>>p;
            if (top != NULL) change(); break;
        }
        case 6:
        {
            if (top != NULL) November_and_December(); break;
        }
        case 7: if (top != NULL) Average_age(); break;
 
        default:break;
        }
    } while (l != 8);
}

//псевдокод
auto bad = top;
top = top->next;
 
delete bad;