Каким образом можно записать стек и очередь в дек

# include <iostream.h>
# include <process.h>
# include <conio.h>
 
struct liststruct {
    int numbers, numberq;
    struct liststruct *nexts, *nextq;
};
 
class linelist {
    liststruct *lists, *listq, *heads, *headq;
 
public:
    linelist() {
    heads = 0;
    headq = 0;
    }
    void pushs();
    void views();
    void pops();
 
    void pushq();
    void viewq();
    void popq();
};
 
void linelist::pushs() {
    clrscr();
    liststruct *newnode;
    newnode = new liststruct;
    cout << " Input element : ";
    cin >> newnode->numbers;
    lists = heads;
    if (heads == 0) {
    heads = newnode;
    newnode->nexts = 0;
    }
    else {
    newnode->nexts = lists;
    lists = newnode;
    heads = newnode;
    }
}
 
void linelist::views() {
    clrscr();
    if (heads == 0) {
    cout << " Stack is empty. Press any key to continue..." << endl;
    }
    lists = heads;
    while (lists != 0) {
    cout << " Stack [n] : " << lists->numbers << endl;
    lists = lists->nexts;
    }
}
 
void linelist::pops() {
    clrscr();
    if (heads == 0) {
    cout << " Stack is empty. Press any key to continue..." << endl;
    }
    else {
    cout << " Stack [n] : " << heads->numbers << " => Deleted...";
    heads = heads->nexts;
    }
}
 
void linelist::pushq() {
    clrscr();
    liststruct *newnode;
    newnode = new liststruct;
    cout << " Input element : ";
    cin >> newnode->numberq;
    listq = headq;
    if (headq == 0) {
    headq = newnode;
    newnode->nextq = 0;
    }
    else {
    newnode->nextq = listq;
    listq = newnode;
    headq = newnode;
    }
}
 
void linelist::viewq() {
    clrscr();
    if (headq == 0) {
    cout << " Queue is empty. Press any key to continue..." << endl;
    }
    listq = headq;
    while (listq != 0) {
    cout << " Queue [n] : " << listq->numberq << "\t";
    listq = listq->nextq;
    }
}
 
void linelist::popq() {
    clrscr();
    if (headq == 0) {
    cout << " Queue is empty. Press any key to continue..." << endl;
    return;
    }
    else {
    listq = headq;
 
    if (listq->nextq == 0) {
        cout << " Queue [n] : " << headq->numberq << " => Deleted...";
        headq = 0;
        delete(listq);
        listq = 0;
        return;
    }
    while (listq->nextq->nextq != 0) {
        listq = listq->nextq;
    }
    cout << " Queue [n] : " << listq->nextq->numberq << " => Deleted...";
    delete(listq->nextq);
    listq->nextq = 0;
    }
}
 
 
int main() {
    clrscr();
    linelist ll;
    int l = 0, i;
    char q;
    const char menu[][45] = {
    " 1) Add element to Stack", " 2) Delete element from Stack",
    " 3) View Stack", " 4) Add element to Queue",
    " 5) Delete element from Queue", " 6) View Queue",
    " 7) Convert Stack&Queue to Deq", " 8) View Deq", " 9) Exit"
    };
    while (1) {
    clrscr();
    for (i = 0; i < 9; i++) {
        gotoxy(28, i + 8);
        cputs(menu[i]);
    }
    gotoxy(28, l + 8);
    textcolor(0);
    textbackground(7);
    cputs(menu[l]);
    textcolor(7);
    textbackground(0);
    q = getch();
    switch(q) {
    case 13:
        switch(l) {
        case 0:
        ll.pushs();
        break;
        case 1:
        ll.pops();
        getch();
        break;
        case 2:
        ll.views();
        getch();
        break;
        case 3:
        ll.pushq();
        break;
        case 4:
        ll.popq();
        getch();
        break;
        case 5:
        ll.viewq();
        getch();
        break;
        case 6:
        break;
        case 7:
        break;
        case 8:
        return 0;
        }
        break;
    case 72:
        if (l)
        l--;
        break;
    case 80:
        if (l < 8)
        l++;
        break;
    }
    }
}