The document discusses circular queue data structures. It defines a circular queue as overcoming limitations of simple queues by assuming the queue is circular in nature with the final address following the first. It presents algorithms for insertion and deletion in a circular queue using both array and linked list implementations. It also covers primitive operations like checking for overflow and underflow conditions.

1. Lecture Notes Data Structures and Algorithms
Barani Institute of Information Technology, Rawalpindi 1/4
Week 12
Contents
• Circular Queue
• Primitive Operations of Circular Queue
• Array Implementation of Circular Queue
• Link List Implementation of Circular Queue
Circular Queue
This is another useful representation of a queue is circular which overcomes the limitations of
simple queues. In this way we assume that our queue is circular in nature, means final address is
followed by first address.
Here we arrange the element queue[1], queue[2],…..,queue[n] in a circular fashion, with
queue[1] follows queue[n]. Following fig. illustrates such a representation.
Primitive Operations of Circular Queue
ALGORITHM (Circularqueuedelete)
If front = -1
Then queue underflow
Else A = queue[front]
If front = rear
Begin
Front = -1
Front
Rear

2. Lecture Notes Data Structures and Algorithms
Barani Institute of Information Technology, Rawalpindi 2/4
Rear = -1
End
Else
If front = maxqueuesize
Then front = 0
Else front = front + 1
ALGORITHM (Circularqueueinsert)
If ((front=1) && (rear = maxqueuesize-1) || (front=rear+1))
Then queue overflow
If (front=-1) [initially empty]
Then rear = 0; front=0
Else if rear = maxqueuesize -1
Then rear =0
Else
Rear=rear+1
Queue[rear]=item
Array Implementation of Circular Queue
class Cqueue
{
int q[10];
int front;
int Rear;
public:
Cqueue() {
front=‐1;
Rear=‐1;
}
void insert(int d) {
if((front==0 && Rear==9) || front==Rear+1)
cout<<"Overflow";
if(front==‐1) {
front=0;
Rear=0;
}
else if(Rear==9) {
Rear=0;
} else {
Rear=Rear+1;
}
q[Rear]=d;
}
int remove() {
if(Rear==‐1) {

3. Lecture Notes Data Structures and Algorithms
Barani Institute of Information Technology, Rawalpindi 3/4
cout<<"Overflow";
return;
}
int n=q[front];
q[front]=NULL;
if(front==Rear) {
front=‐1;
Rear=‐1;
} else if(front==9) {
front=0;
} else
front=front+1;
return n;
}
};
Link List Implementation of Circular Queue
struct link
{
int data;
link *next;
};
class CQueue
{
link *front;
public:
CQueue() {
front=NULL;
}
void Insert(int d) {
link *newlink=new link;
newlink‐>data=d;
if(front==NULL) {
front=newlink;
newlink‐>next=front;
} else {
link *current=front;
while(current‐>next!=front)
{
current=current‐>next;
}
current‐>next=newlink;
newlink‐>next=front;
}
}

4. Lecture Notes Data Structures and Algorithms
Barani Institute of Information Technology, Rawalpindi 4/4
int remove() {
if(front==NULL) {
cout<<"EMPTY";
} else {
link *temp=front;
front=front‐>next;
link *current=front;
while(current‐>next!=temp)
{
current=current‐>next;
}
int n=temp‐>data;
current‐>next=front;
delete temp;
return n;
}
}
};