下面代码实现的一个功能是模拟ATM，程序允许用户输入3个数据：队列的最大长度、程序模拟的持续时间（单位为小时）以及平均每小时的客户数。
在程序中，使用循环，每次循环代表一分钟，在每次循环中，程序将完成下面的工作
1.是否来新客户，来：队列未满，入队；队列已满，拒绝
2.如果没有客户进行交易，则取队列的第一个客户。确定客户的已等候时间，并将wait_time计数器设置为新客户所需的处理时间
3.如果客户正在处理中，则讲wait_time计数器减1.
4.记录各种数据，如获得服务的客户数目、被拒绝的客户数（满队情况）、排队等候的累计时间以及累积的队列长度等。
queue.h
//queue.h --interface for a queue #ifndef QUEUE_H_ #define QUEUE_H_ //This queue will contain Customer items class Customer { private: long arrive; // arrive time for customer int processtime;//processing time for customer public: Customer() {arrive = processtime = 0;} void set(long when); long when() const {return arrive;} int ptime() const {return processtime; } }; typedef Customer Item; class Queue { private: //class scope definitions //Node is a nested structure definition local to this c struct Node{Item item; struct Node *next;}; enum {Q_SIZE = 10}; //private class members Node * front; // pointer to front of Queue Node * rear; // pointer to rear of Queue int items; // current number of items in Queue const int qsize; // maximum number of items in Queue //preemptive definitions to prevent public copying Queue(const Queue & q) : qsize(0) {} Queue & operator = (const Queue & q) {return *this;} public: Queue(int qs = Q_SIZE); // create queue with a qs limit ~Queue(); bool isempty() const; bool isfull() const; int queuecount() const; bool enqueue(const Item &item); // add item to end bool dequeue(Item &item); }; #endifqueue.cpp
//queue.cpp --Queue and Customer methods #include <cstdlib> #include "queue.h" //Queue methods Queue::Queue(int qs) : qsize(qs) { front = rear = NULL; //or nullptr items = 0; } Queue::~Queue() { Node * temp; while (front != NULL) //while the queue is not yet empty { temp = front; // save the address of front item front = front->next;// reset pointer to next item delete temp; // delete former front } } bool Queue::isempty() const { return items == 0; } bool Queue::isfull() const { return items == qsize; } int Queue::queuecount() const { return items; } //add item to queue bool Queue::enqueue(const Item& item) { if(isfull()) return false; Node *add = new Node; // create node // on failure, new throws std::bad_alloc exception add->item = item; // set node pointers add->next =NULL; // or nullptr items++; if(front == NULL) // if queue is empty front = add; // place item at front else rear->next = add; // else place at rear rear = add; // have rear point to new node return true; } //place front item into item variable and remove from queue bool Queue::dequeue(Item& item) { if(front == NULL) return false; item = front->item; // set item to first item in queue items--; Node * temp = front; // save location of first item front = front->next; // rest front to next item delete temp; // delete former first item if(items == 0) rear = NULL; return true; } //time set to a random value in the range 1-3 void Customer::set(long when) { processtime = std::rand() % 3 + 1; arrive = when; }main.cpp
//main.cpp -- using the queue interface //compile with queue.cpp #include <iostream> #include <cstdlib> // for rand() and srand() #include <ctime> // for time() #include "queue.h" const int MIN_PER_HR = 60; bool newcustomer(double x); // is there a new customer? int main(int argc, char **argv) { using std::cin; using std::cout; using std::endl; using std::ios_base; //set things up std::srand(std::time(0)); //random initializing of rand() cout << " Case study: Bank of Heather Automatic Teller \n"; cout << "Enter maximum size of queue: "; int qs; cin >> qs; Queue line(qs); // line queue holds up to qs people cout << "enter the number of simulation hours: "; int hours; //hours of simulation cin >> hours; // simulation will run 1 cycle per minute long cyclelimit = MIN_PER_HR * hours; // # of cycles cout << "enter the average number of customer per hour : "; double perhour; //average # of arrival per hour cin >> perhour; double min_per_cust; //average time between arriavals min_per_cust = MIN_PER_HR / perhour; Item temp; //new customer data long turnaways = 0;// turned away by full queue long customers = 0;// joined the queue long served = 0;// served during the simulation long sum_line = 0;// cumulative line length int wait_time = 0;// time until autoteller is free long line_wait = 0;//cumulative time in line //running the simulation for(int cycle = 0; cycle < cyclelimit; cycle++) { if(newcustomer(min_per_cust))//have new customer { if(line.isfull()) turnaways++; else{ customers++; temp.set(cycle);//cycle = time of arrival line.enqueue(temp);// add newcomer to line } } if(wait_time <= 0 && !line.isempty()) { line.dequeue(temp);//attend next customer wait_time = temp.ptime();//for wait_time minutes line_wait += cycle - temp.when(); served++; } if(wait_time > 0) wait_time--; sum_line += line.queuecount(); } //reporting results if(customers > 0) { cout << " customers accepted : " << customers << endl; cout << " customers served : " << served << endl; cout << " turnaways : " << turnaways << endl; cout << " average queue size : "; cout.precision(2); cout << (double) sum_line / cyclelimit << endl; cout << " average wait time : " << (double) line_wait /served << " minutes\n"; } else cout << " No customers!\n"; cout << " Done! \n "; return 0; } //x = average time in minutes, between customers // return value is true if customer shoews up this minute bool newcustomer(double x) { return (std::rand() * x / RAND_MAX < 1); }最后模拟的结果，如下图所示
可以看到如果一个小时客户的平均数量在15个时，拒绝的客户为0；等候时间也只有0.58min，但是如果将一个小时客户的平均数量设置在30个，等候的平均时间就会大大增加。这里因为采取随机数，所以每次结果可能会有一些不同。
同时，也练习了单链表的构建。链表是一种数据的存储方式，其保存的数据在内存中是不连续的，采用指针对数据进行访问，代码中这个写的非常清楚，而且也使用了很多次。
队列是一种数据结构，其特点是先进先出（正是因为如此，才特别符合ATM的模拟）。
参考书籍
Publishing S. C++ Primer Plus, Fifth Edition[J]. Pearson Schweiz Ag, 2005.
