C++ Primer Plus第六版编程练习12.6解答

queue.h

// queue.h -- interface for a queue#ifndef QUEUE_H_#define QUEUE_H_// This queue will contain Customer itemsclass Customer{private:    long arrive;        // arrival time for customer    int processtime;    // processing time for customerpublic:    Customer() : arrive(0), 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 class    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);       // remove item from front};#endif

queue.cpp

// queue.cpp -- Queue and Customer methods#include "queue.h"#include <cstdlib>         // (or stdlib.h) for rand()// Queue methodsQueue::Queue(int qs) : qsize(qs){    front = rear = NULL;    // or nullptr    items = 0;}Queue::~Queue(){    Node * temp;    while (front != NULL)   // while queue is not yet empty    {        temp = front;       // save 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 queuebool 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 queuebool 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;    // reset front to next item    delete temp;            // delete former first item    if (items == 0)        rear = NULL;    return true;}// customer method// when is the time at which the customer arrives// the arrival time is set to when and the processing// time set to a random value in the range 1 - 3void Customer::set(long when){    processtime = std::rand() % 3 + 1;    arrive = when; }

bank.cpp

// bank.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(){    using std::cin;    using std::cout;    using std::endl;    using std::ios_base;// setting 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 line1(qs);         // line queue holds up to qs people    Queue line2(qs);    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    Item temp;          //  new customer data    long turnaways;     //  turned away by full queue    long customers;     //  joined the queue    long served;        //  served during the simulation    long sum_line;      //  cumulative line length    long wait_time;     //  time until autoteller is free    long line_wait;     //  cumulative time in line    long cycle;         //  running time    cout << "Enter the average number of customers per hour: ";    double perhour;         //  average # of arrival per hour    double min_per_cust;    //  average time between arrivals    while (cin >> perhour)    {        turnaways = 0;        customers = 0;        served = 0;        sum_line = 0;        wait_time = 0;        line_wait = 0;        min_per_cust = MIN_PER_HR / perhour;        // running the simulation        for (cycle = 0; cycle < cyclelimit; cycle++)        {            if (newcustomer(min_per_cust))  // have newcomer            {                if (line1.isfull() && line2.isfull())                    turnaways++;                else  // line1 or line2 is not full                {                    customers++;                    temp.set(cycle);    // cycle = time of arrival                    // if line1 has less customers than line2, add new customer to line1, else add to line2                    if(line1.queuecount()<=line2.queuecount())                        line1.enqueue(temp);                    else                        line2.enqueue(temp);                }            }            // process customers in first queue            if (wait_time <= 0 && !line1.isempty())            {                line1.dequeue (temp);      // attend next customer                wait_time = temp.ptime(); // for wait_time minutes                line_wait += cycle - temp.when();                served++;            }            // process customers in second queue            if (wait_time <= 0 && !line2.isempty())            {                line2.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 += ( line1.queuecount() + line2.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.setf(ios_base::fixed, ios_base::floatfield);            cout << (double) sum_line / cyclelimit << endl;            cout << " average wait time: "                 << (double) line_wait / served << " minutes\n";        }        else            cout << "No customers!\n";        // clear queues        while (!line1.isempty())            line1.dequeue(temp);        while (!line2.isempty())            line2.dequeue(temp);        cout << "\nEnter the average number of customers per hour(q to quit): ";    }    cout << "Done!\n";    cin.get();    return 0;}//  x = average time, in minutes, between customers//  return value is true if customer shows up this minutebool newcustomer(double x){    return (std::rand() * x / RAND_MAX < 1);}