Question: 13.21//This is the header file queue.h. This is the interface for the class Queue, 2 //which is a class for a queue of symbols. 3

13.21//This is the header file queue.h. This is the interface for the class Queue,

2 //which is a class for a queue of symbols.

3 #ifndef QUEUE_H

4 #define QUEUE_H

5 namespace queuesavitch

6 {

7 struct QueueNode

8 {

9 char data;

10 QueueNode *link;

11 };

12 typedef QueueNode* QueueNodePtr;

14 class Queue

15 {

16 public:

17 Queue();

18 //Initializes the object to an empty queue.

19 Queue(const Queue& aQueue);

20 ~Queue();

21 void add(char item);

22 //Postcondition: item has been added to the back of the queue.

23 char remove();

24 //Precondition: The queue is not empty.

25 //Returns the item at the front of the queue and

26 //removes that item from the queue.

27 bool empty() const;

28 //Returns true if the queue is empty. Returns false otherwise.

29 private:

30 QueueNodePtr front; //Points to the head of a linked list.

31 //Items are removed at the head

32 QueueNodePtr back; //Points to the node at the other end of the

33 //linked list. Items are added at this end.

34 };

35 }//queuesavitch

36 #endif //QUEUE_H

13.22//Program to demonstrate use of the Queue class.

2 #include

3 #include "queue.h"

4 using namespace std;

5 using namespace queuesavitch;

7 int main()

8 {

9 Queue q;

10 char next, ans;

12 do

13 {

14 cout << "Enter a word: ";

15 cin.get(next);

16 while (next != ' ')

17 {

18 q.add(next);

19 cin.get(next);

20 }

22 cout << "You entered:: ";

23 while ( ! q.empty() )

24 cout << q.remove();

25 cout << endl;

27 cout << "Again?(y/n): ";

28 cin >> ans;

29 cin.ignore(10000, ' ');

30 } while (ans !='n' && ans != 'N');

32 return 0;

13.23/This is the implementation file queue.cpp.

2 //This is the implementation of the class Queue.

3 //The interface for the class Queue is in the header file queue.h.

4 #include

5 #include

6 #include

7 #include "queue.h"

8 using namespace std;

10 namespace queuesavitch

11 {

12 //Uses cstddef:

13 Queue::Queue() : front(NULL), back(NULL)

14 {

15 //Intentionally empty.

16 }

18 Queue::Queue(const Queue& aQueue)

(

Queue::~Queue()

24 //Uses cstddef:

25 bool Queue::empty() const

26 {

27 return (back == NULL); //front == NULL would also work

28 }

30 //Uses cstddef:

31 void Queue::add(char item)

32 {

33 if (empty())

34 {

35 front = new QueueNode;

36 front->data = item;

37 front->link = NULL;

38 back = front;

39 }

41 else

42 {

43 QueueNodePtr temp_ptr;

44 temp_ptr = new QueueNode;

45 temp_ptr->data = item;

46 temp_ptr->link = NULL;

47 back->link = temp_ptr;

48 back = temp_ptr;

49 }

50 }

52 //Uses cstdlib and iostream:

53 char Queue::remove()

54 {

55 if (empty())

56 {

57 cout << "Error: Removing an item from an empty queue. ";

58 exit(1);

59 }

61 char result = front->data;

63 QueueNodePtr discard;

64 discard = front;

65 front = front->link;

(

if (front == NULL) //if you removed the last node

67 back = NULL;

69 delete discard;

71 return result;

72 }

73 }//queuesavitch

Modify or rewrite the Queue class (Display 13.21 through 13.23) to simulate

customer arrivals at the Department of Motor Vehicles (DMV) counter.

As customers arrive, they are given a ticket number starting at 1 and

incrementing with each new customer. When a customer service agent is

free, the customer with the next ticket number is called. This system results

in a FIFO queue of customers ordered by ticket number. Write a program

that implements the queue and simulates customers entering and leaving

the queue. Input into the queue should be the ticket number and a

timestamp when the ticket was entered into the queue. A ticket and its corresponding

timestamp is removed when a customer service agent handles

the next customer. Your program should save the length of time the last

three customers spent waiting in the queue. Every time a ticket is removed

from the queue, update these times and output the average of the last three

customers as an estimate of how long it will take until the next customer is

handled. If nobody is in the queue, output that the line is empty.

Code to compute a timestamp based on the computers clock is given

below. The time(NULL) function returns the number of seconds since

January 1, 1970, on most implementations of C++:

#include

...

int main()

{

long seconds;

seconds = static_cast(time(NULL));

cout << "Seconds since 1/1/1970: " << seconds << endl;

return 0;

}

Sample execution is shown here:

The line is empty.