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Message: [QUOTE="Robert, post: 3044636"] dear sir: I have read the c++ primer plus 5 book, and do the chapter 12 programming exercises question 5, but the average_wait have negative result. I don't understand why? here is the code, thank you anyone replay me.:) /************************* customer.h *************************/ #ifndef CUSTOMER_H_ #define CUSTOMER_H_ class Customer { private: long arrive; //arrival time for customer int processtime; //process time for customer public: Customer() { arrive = processtime = 0; } void set(long when); long when() const { return arrive; } int ptime() const { return processtime; } }; #endif /************************* customer.cpp *************************/ #include <iostream> #include "customer.h" //when is the time at which the customer arrives //the arrival times is set to when and the processing //time set to a random value in the range 1 - 3 void Customer::set(long when) { processtime = std::rand() % 3 + 1; arrive = when; } /************************* queue.h *************************/ #ifndef QUEUE_H_ #define QUEUE_H_ #include "customer.h" namespace QUEUE { 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 definitiond 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 *************************/ #include "queue.h" #include <cstdlib> namespace QUEUE { //Queue methods Queue::Queue(int qs):qsize(qs) { front = rear = NULL; 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 queue bool Queue::enqueue(const Item & item) { if (isfull()) return false; Node * add = new Node; //create node if (add == NULL) return false; //quit if none available add->item = item; //set node pointers add->next = NULL; 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 frony item into item variable and remove fron a 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;//reset front to next item delete temp; //delete former first item if ( items == 0) rear = NULL; return true; } } /************************* main.cpp *************************/ #include <iostream> #include <cstdlib> //for rand() and srand() #include <ctime> //for time() #include "queue.h" bool newcustomer(double x); //is there a new customer? void main() { const int MIN_PER_HR = 60; using namespace std; using namespace QUEUE; srand(static_cast<unsigned int>(time(0))); cout << "Case Study: Bank of Healther Automatic Teller\n"; cout << "Enter maximum size of quiue: "; int qs; cin >> qs; Queue line(qs); cout << "Enter the number of simulation hours: "; int hours; cin >> hours; long cyclelimit = MIN_PER_HR * hours; //cout << "Enter the average number of customers per hour: "; double perhour; //cin >> perhour; double min_per_cust; Item temp; long turnaways = 0; long customers = 0; long served = 0; long sum_line = 0; int wait_time = 0; long line_wait = 0; long double average_wait = 0; for (long mpc = 0; mpc < LONG_MAX; mpc++) { average_wait = 0; for (int cycle = 0; cycle < cyclelimit; cycle++) { if (newcustomer(mpc)) { if (line.isfull()) turnaways++; else { customers++; temp.set(cycle); line.enqueue(temp); } } if (wait_time <= 0 && !line.isempty()) { line.dequeue(temp); wait_time = temp.ptime(); line_wait += cycle - temp.when(); served++; } if (wait_time > 0) wait_time--; sum_line += line.queuecount(); } if (served) average_wait = (double)line_wait / served; if (served && average_wait <= 1.00) { perhour = mpc; break; } } 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.setf(ios_base::showpoint); cout << (double) sum_line / cyclelimit << endl; cout << " average wait time: " << (double) line_wait / served << "minutes\n"; cout << "the average number of customers per hour" << perhour << endl; } else cout << "No customers!\n"; } bool newcustomer(double x) { return ( rand() * x / RAND_MAX < 1); } [/QUOTE]

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