[求助]数字1，2，3，4顺序入栈，问有多少种出栈方式。

用的是Thinging in C++上的Stack类


这是头文件
//: C06:Stack3.h
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 2000
// Copyright notice in Copyright.txt
// With constructors/destructors
#ifndef STACK3_H
#define STACK3_H

class Stack {
struct Link {
void* data;
Link* next;
Link(void* dat, Link* nxt);
~Link();
}* head;
public:
Stack();
~Stack();
void push(void* dat);
void* peek();
void* pop();
};
#endif // STACK3_H ///:~


这是Stack的定义
//: C06:Stack3.cpp {O}
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 2000
// Copyright notice in Copyright.txt
// Constructors/destructors
#include "Stack3.h"
#include "../require.h"
using namespace std;

Stack::Link::Link(void* dat, Link* nxt) {
data = dat;
next = nxt;
}

Stack::Link::~Link() { }

Stack::Stack() { head = 0; }

void Stack::push(void* dat) {
head = new Link(dat,head);
}

void* Stack::peek() {
require(head != 0, "Stack empty");
return head->data;
}

void* Stack::pop() {
if(head == 0) return 0;
void* result = head->data;
Link* oldHead = head;
head = head->next;
delete oldHead;
return result;
}

Stack::~Stack() {
require(head == 0, "Stack not empty");
} ///:~


这是测试Stack的一个例子,实现倒序输出,我现在就死用上面的资源文件实现“数字1，2，3，4顺序入栈，问有多少种出栈方式？”
//: C06:Stack3Test.cpp
// From Thinking in C++, 2nd Edition
// Available at http://www.BruceEckel.com
// (c) Bruce Eckel 2000
// Copyright notice in Copyright.txt
//{L} Stack3
//{T} Stack3Test.cpp
// Constructors/destructors
#include "Stack3.h"
#include "../require.h"
#include <fstream>
#include <iostream>
#include <string>
using namespace std;

int main(int argc, char* argv[]) {
requireArgs(argc, 1); // File name is argument
ifstream in(argv[1]);
assure(in, argv[1]);
Stack textlines;
string line;
// Read file and store lines in the stack:
while(getline(in, line))
textlines.push(new string(line));
// Pop the lines from the stack and print them:
string* s;
while((s = (string*)textlines.pop()) != 0) {
cout << *s << endl;
delete s;
}
} ///:~



谢谢！！！！！！