problem with stack structure in C++(using pointer), plz help !!!

[C++ Programming]

#include
using namespace std;

class Element{

public:
int value;
Element *next;

Element() : value(0), next(NULL) {}
Element(int v) : value(v), next(NULL) {}
Element(int v,Element *n) : value(v), next(n) {}
};

class Stack{

private:
int length;
Element head;

public:
Stack() : head(), length(0) {}

void clear();
void traversal() const;
void push(int value);
int pop();
};


void Stack::clear(){
head = Element();
}

void Stack::traversal() const{
if (length == 0)
cout