My stack

#include <iostream>
#include <string>
#include <fstream>
#include <exception>

#define myStack
#define myAlg

using namespace std;



#ifdef myStack
template<class T>
class Stack {

struct Node {

    Node(T el, Node * node)
    {
        data = el;
        next = node;
    }
    Node* next;
    T data;
};

Node* _top;
int _size;

public:
    Stack()
    {
        _top = NULL;
        _size = 0;
    }
    ~Stack()
    {
        while (_top != NULL && _top->next != NULL)//_top != NULL <=> _size > 0
        {
            Node* temp = _top;
            _top = _top->next;
            delete temp;
        }
    }

    void push(T el);
    void pop();
    T top();
    int size();
    T peek();

    bool empty();

};
#endif
#ifdef myAlg
template<class T>
bool Stack<T>::empty()
{
    return !_size;
}

template<class T>
T Stack<T>::peek()
{
    if (!_size)
        return NULL;
    return _top->data;
}

template<class T>
int Stack<T>::size()
{
    return _size;
}
template<class T>

T Stack<T>::top()
{
    try
    {
        if (_top == NULL)
            throw out_of_range("Error: Stack is empty!");
        return _top->data;
    }
    catch (exception &e)
    {
        cout << e.what() << endl;
    }
}

template<class T>
void Stack<T>::pop() {
    Node* temp = _top;
    _top = _top->next;
    delete temp;
    _size--;

}
template<class T>
void Stack<T>::push(T el)
{
    Node * temp = new Node(el, _top);
    _top = temp;
    _size++;
}
#endif // myAlg


int main()
{


}