Linked Stack.h

#include <iostream>
using namespace std;

struct SinglyNode
{
    string elem;      // element value
    SinglyNode *next; // next item in the list
};

struct SinglyLinkedList
{
    SinglyNode *head; // pointer to the head of list

    SinglyLinkedList();  // empty list constructor
    ~SinglyLinkedList(); // destructor

    bool empty() const;             // is list empty?
    const string &front() const;    // get front element
    void addFront(const string &e); // add to front of list
    void removeFront();             // remove front item list
};

void SinglyLinkedList::removeFront()
{                           // remove front item
    SinglyNode *old = head; // save current head
    head = old->next;       // skip over old head
    delete old;             // delete the old head
}

void SinglyLinkedList::addFront(const string &e)
{                                   // add to front of list
    SinglyNode *v = new SinglyNode; // create new node
    v->elem = e;                    // store data
    v->next = head;                 // head now follows v
    head = v;                       // v is now the head
}

SinglyLinkedList::SinglyLinkedList() // constructor
{
    head = NULL;
}

SinglyLinkedList::~SinglyLinkedList() // destructor
{
    while (!empty())
        removeFront();
}

bool SinglyLinkedList::empty() const // is list empty?
{
    return head == NULL;
}

const string &SinglyLinkedList::front() const // get front element
{
    return head->elem;
}

struct LinkedStack // stack as a linked list
{
    SinglyLinkedList S; // linked list of elements
    int n;              // number of elements

    LinkedStack();      // constructor
    int size() const;   // number of items in the stack
    bool empty() const; // is the stack empty?

    const string &top() const;  // the top element
    void push(const string &e); // push element onto stack
    void pop();                 // pop the stack
};

LinkedStack::LinkedStack() : S(), n(0) // constructor
{
}

int LinkedStack::size() const // number of items in the stack
{
    return n;
}

bool LinkedStack::empty() const // is the stack empty?
{
    return n == 0;
}

const string &LinkedStack::top() const // return top of stack
{
    if (empty())
    {
        cout << "Top of empty stack !" << endl;
        return 0;
    }
    return S.front();
}

void LinkedStack::push(const string &e) // push element onto the stack
{
    ++n;
    S.addFront(e);
}

void LinkedStack::pop() // pop the stack
{
    if (empty())
    {
        cout << "Pop from empty stack !" << endl;
        return;
    }
    --n;
    S.removeFront();
}