Lista dupla

#include <iostream>
#include <fstream>
#include <malloc.h>

using namespace std;

typedef struct _node {
    int x;
    struct _node *prox;
} node;

node *head;
node *tail;

node* cria() {
    node *aux;
    aux = (node*)malloc(sizeof(node));
    head = aux;
    tail = head;
    return head;

}

node* insereFIM(node *lst, int x) {
    node *aux;
    aux = (node*)malloc(sizeof(node));
    aux->x = x;
    aux->prox = NULL;
    tail->prox = aux;
    tail = aux;
    return head;

}

node* insereINI(node *lst, int x) {
    node *aux;
    aux = (node*)malloc(sizeof(node));
    aux->prox = head;
    head->x = x;
    head = aux;
    return head;
}

void mostra(node *lst) {
    node *aux;
    aux = lst->prox;
    while (aux != NULL) {
        cout << aux->x << "\n";
        aux = aux->prox;

    }

}

node* removeINI(node *lst) {
    node *aux;
    cout << "\n Elemento removido: " << lst->prox->x << "\n";
    aux = head;
    head = head->prox;
    free(aux);
    return head;
}


node* removeFIM(node *lst) {
    node *aux;
    node *ant;
    aux = lst->prox;
    while (aux->prox != NULL) {
        ant = aux;
        aux = aux->prox;
    }

    cout << "\n Elemento removido: " << aux->x << "\n";

    tail = ant;
    tail->prox = NULL;
    free(aux);
    return head;

}

int main() {
    system("MODE CON: LINES=50");
    system("CLS");

    node *lista;
    int x, y;

    lista = cria();

    for (int i=0; i<5; i++){
        cout << "\n Digite o valor " << i+1 << ": ";
        cin >> x;
        lista = insereFIM(lista, x);
    }

    mostra(lista);
    lista = removeFIM(lista);
    mostra(lista);
    cout << "\n";

    for (int i=0; i<5; i++){
        cout << "\n Digite o valor " << i+1 << ": ";
        cin >> x;
        lista = insereINI(lista, x);
    }
    cout << "\n\n";
    mostra(lista);
    lista = removeINI(lista);
    mostra(lista);
    cout << "\n\n";
    // lê lista de um arquivo
    ifstream txt("num.txt");
    while(txt >> y) {
        lista = insereINI(lista, y);
    }
    mostra(lista);

    system("pause");

}