Struct double linked list stack swap pointer file header

//---------------------------------------------------------------->> File Headers
#ifndef HEADERS_H_INCLUDED
#define HEADERS_H_INCLUDED

#include <iostream>

using namespace std;

struct mahasiswa{
    string nama;
    int npm;
};

struct node{
    mahasiswa mhs;
    node *next;
    node *prev;
};

node *baru,*bantu,*awal=NULL,*akhir=NULL;

bool cekAkhirNull(){
    return akhir == NULL;
}

bool cekAwalNull(){
    return awal==NULL;
}

#endif // HEADERS_H_INCLUDED

//---------------------------------------------------------------->> End of File Headers
//---------------------------------------------------------------->> main.cpp
#include <iostream>
#include <stdlib.h>
#include "headers.h"

using namespace std;

void push(){
    baru = new node;
    baru->next = NULL;
    baru->prev = NULL;
    cout << "Masukkan nama : ";
    cin.sync();
    getline(cin,baru->mhs.nama);
    cout << "Masukkan NPM : ";
    cin.sync();
    cin >> baru->mhs.npm;

    if(cekAwalNull()){
        awal=akhir=baru;
    }else{
        akhir->next = baru;
        baru->prev = akhir;
        akhir = baru;
    }
}

void pop(){
    if(cekAkhirNull()){
        cout << "Data kosong" << endl;
        system("pause");
    }else{
        cout << "Data " << akhir->mhs.nama << " Telah dihapus " << endl;
        system("pause");
        if(akhir->prev == NULL){
            awal=akhir=NULL;
        }else{
            bantu = akhir;
            akhir = akhir->prev;
            akhir->next = NULL;
            delete bantu;
        }
    }
}

void view(){
    bantu = awal;
    while(bantu!=NULL){
        cout << "[" << bantu->mhs.nama << "," << bantu->mhs.npm << "] ";
        bantu = bantu->next;
    }
}

void tukar(){
    if(akhir->prev == awal){
        cout << "Data tertukar : ";
        bantu = akhir;
        akhir->next = awal;
        akhir->prev = NULL;

        awal->prev = akhir;
        awal->next = NULL;

        akhir = awal;
        awal = bantu;

        view();
    }else if(awal == akhir){
        cout << "Data hanya 1, tidak dapat di tukar " << endl;
    }else{
        cout << "Data tertukar : ";
        bantu = akhir->prev;
        bantu->prev->next = akhir;
        akhir->prev = bantu->prev;
        akhir->next = bantu;
        bantu->prev = akhir;
        bantu->next = NULL;
        akhir = bantu;
        view();
    }
    cout << endl;
    system("pause");
}

int main()
{
    int menu;
    do{
        system("cls");
        view();
        cout << endl;
        cout << "Menu :" << endl;
        cout << "1. Push" << endl;
        cout << "2. Pop" << endl;
        cout << "3. Tukar data terakhir dengan terakhir-1" << endl;
        cout << "4. Keluar" << endl;
        cout << "Masukkan menu : ";
        cin >> menu;


        if(menu == 1){
            push();
        }else if(menu == 2){
            pop();
        }else if(menu == 3){
            tukar();
        }
    }while(menu != 4);
}

//---------------------------------------------------------------->> End of main.cpp