The document discusses dynamic queues implemented as linked lists. It describes how queues follow a FIFO ordering and the common enqueue and dequeue operations. It then explains how to implement a dynamic queue using pointers to track the front and rear nodes. Functions for enqueue, dequeue, getFront and isEmpty are presented, showing how the queue size adjusts dynamically as nodes are added or removed. The document concludes with an example use of queues in simulations.

1. z
Presentation Topic
Dynamic Queue.

2. z
Queues
 A Queue is a special kind of list, where
items are inserted at one end (the rear)
And deleted at the other end (the front).
 Accessing the elements of queues follows
a First In First Out (FIFO) order.
 Example
 Like customers standing in a check-out
line in a store, the first customer in is
the first customer served.
2

3. z
Common Operations on Queues
 getFRONT(Q): Returns the first element on
Queue Q.
 ENQUEUE(x,Q): Inserts element x at the
end of Queue Q.
 DEQUEUE(Q): Deletes the first element of
Q.
 ISEMPTY(Q): Returns true if and only if Q
is an empty queue.
 ISFULL(Q): Returns true if and only if Q is
full.
3

4. z
Enqueue and Dequeue
 Primary queue operations: Enqueue and
Dequeue
 Enqueue – insert an element at the rear of
the queue.
 Dequeue – remove an element from the
front of the queue.
4

5. z
Queues Implementations
Static:
Queue is implemented by an array, and size
of queue remains fix
Dynamic:
A queue can be implemented as a linked
list and expand or shrink with each enqueue
or dequeue operation.
5

6. z
Static Implementation of Queues
6

7. z
Dynamic Implementation of Queues
Dynamic implementation is done using pointers.
• Front : A pointer to the first element of the
queue.
• Rear : A pointer to the last element of the
queue.
7
x y z
Front
Rear
.

8. z
Dynamic Implemenatation
• Enqueue (X)
• Enqueue (Y)
8
Q.front
Q.Rear
.
x
Q.front
Q.Rear
x .
y

9. z
Dynamic Implementation
• Dequeue:
• MakeNULL:
9
Q.front
Q.Rear
.
y
Q.front
Q.Rear
NULL

10. z
Dynamic implementation of Queue
struct queueNode
{
int num;
queueNode next;
};
queueNode front = NULL;
queueNode rear = NULL;
class dynQueue{
int size;
10
public:
dynQueue();
void enqueue();
void dequeue();
bool isEmpty();
void displayQueue();
void makeNull();
};

11. z
Constructor
dynQueue()
{
size=0;
}
11

12. z Enqueue( ) Function
Void enqueue(int x)
{
/*Linked list node*/
queueNode *n = new Node();
n->setData(x);
n->Next= NULL;
12
if (front == NULL)
{
front = n;
rear = n;
size++;
}
else
{
rear->Next=n;
rear = n;
size++;
}
}

13. z
Dequeue( ) Function
int dequeue()
{
if(front == NULL)
{
cout<<“Queue is Empty“;
}
else
{ queueNode *temp=front;
int x = front->getData();
front = front->getNext();
Delete temp;
return x;
}
}
13

14. z
getFront() and isEmpty()
int getFront()
{
return front->Data;
}
int isEmpty()
{
return ( front == NULL );
}
14

15. z
Display( ) Function
void display()
{
if(isEmpty())
cout<<“Queue is empty“;
else
{
for (int i=0; i<counter; i++)
cout<<queue[(front+ i)% maxSize];
}
}
15

16. z
Use of Queues
Out of the numerous uses of the queues, one of the most
useful is simulation.
A simulation program attempts to model a real-world
phenomenon.
Many popular video games are simulations, e.g., SimCity,
Flight Simulator.
Each object and action in the simulation has a counterpart in
real world.
16

17. z
Uses of Queues
If the simulation is accurate, the result of the program should
mirror the results of the real-world event.
Thus it is possible to understand what occurs in the real-world
without actually observing its occurrence.
17