Doubly-Linked List

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <locale>
#include <iomanip>
#include <ctime>
#include <cmath>

using namespace std;

struct list
{
    int data;
    list *next, *prev;
};

void list_add(int num, list *&head)
{
    if (head == 0)
    {
        head = new list;
        head->next = 0;
        head->prev = 0;
        head->data = num;
    }
    else
    {
        list *temp = head;
        while (temp->next != NULL)
            temp = temp->next;
        list *p = new list;
        p->data = num;
        p->next = 0;
        p->prev = temp;
        temp->next = p;
        temp = temp->next;
    }
}

bool list_empty(list *head)
{
    if (head == NULL)
        return 1;
    else
        return 0;
}

void list_print(list *head)
{
    if (list_empty(head))
    {
        cout << "Список пуст" << endl;
        return;
    }
    list *temp = head;
    while (temp->next != NULL)
    {
        temp = temp->next;
        cout << temp->data << " ";
    }
    cout << endl;
    temp = head;
}

void list_delete_first(list *&head)
{
    if (list_empty(head))
        return;
    if (head->next == NULL)
    {
        list *temp = head;
        delete temp;
        head = 0;
        return;
    }
    list *temp = head;
    head = head->next;
    head->prev = NULL;
    delete temp;
}

void list_delete_last(list *&head)
{
    if (list_empty(head))
        return;
    if (head->next == NULL)
    {
        list *temp = head;
        delete temp;
        head = 0;
        return;
    }
    list *temp = head;
    while (temp->next != NULL)
        temp = temp->next;
    temp->prev->next = NULL;
    delete temp;
}

void list_delete_n(int pos, list *&head)
{
    if (list_empty(head))
        return;
    if (head->next == NULL)
    {
        list *temp = head;
        delete temp;
        head = 0;
        return;
    }
    if (pos == 1)
    {
        list_delete_first(head);
        return;
    }
    list *temp = head;
    for (int i = 0; i < pos; i++)
        temp = temp->next;
    if (temp->next == NULL)
    {
        list_delete_last(head);
        return;
    }
    temp->next->prev = temp->prev;
    temp->prev->next = temp->next;
    temp->next = 0;
    temp->prev = 0;
    delete temp;
}

void list_delete_with_spec_all(int val, list *&head)
{
    list *temp = head;
    int k = 1;
    while (temp != 0)
    {
        if (temp->data == val)
            if (k == 1)
                list_delete_first(head);
            else if (temp->next == 0)
            {
                list_delete_last(head);
                break;
            }
            else
            {
                temp->next->prev = temp->prev;
                temp->prev->next = temp->next;
                list *kill = temp;
                temp = temp->next;
                k++;
                delete kill;
                continue;
            }
        k++;
        temp = temp->next;
    }
}

void list_delete_spec_first(int val, list *&head)
{
    list *temp = head;
    if (temp->data == val)
    {
        list_delete_first(head);
        return;
    }
    else
    {
        while ((temp->data != val) && (temp->next != 0))
            temp = temp->next;
        if ((temp->next == 0) && (temp->data == val))
        {
            list_delete_last(head);
            return;
        }
        temp->next->prev = temp->prev;
        temp->prev->next = temp->next;
        list *kill = temp;
        temp = temp->next;
        delete kill;
    }
}

void task();
int main()
{
    setlocale(LC_ALL, "Russian");
    task();
    system("pause");
    return 0;
}

void task()
{
    srand(time(0));
    int n;
    cout << "Введите количество элементов списка: ";
    cin >> n;
    list *list_ = 0;
    for (int i = 0; i <= n; i++)
        list_add(i*rand() % 10, list_);
    list_print(list_);
    list_delete_first(list_);
    list_print(list_);
    list_delete_last(list_);
    list_print(list_);
    int pos;
    cout << "Введите позицию элемента, который требуется удалить: ";
    cin >> pos;
    list_delete_n(pos,list_);
    list_print(list_);
    int val;
    cout << "Введите значение, которое требуется удалить: ";
    cin >> val;
    list_delete_with_spec_all(val, list_);
    list_print(list_);
    int val_;
    cout << "Введите значение, которое требуется удалить первым в списке: ";
    cin >> val_;
    list_delete_spec_first(val_, list_);
    list_print(list_);
}