QUES 24 QUEUE

C LANGUAGE BOOK

 Queues


 In a queue, the element deleted is always the one that
has been in the set for the longest time: the queue implements a first-in, first-out,
or FIFO, policy.

We call the INSERT operation on a queue ENQUEUE, and we call the DELETE
operation DEQUEUE; like the stack operation POP,DEQUEUE takes no element ar-
gument. The FIFO property of a queue causes it to operate like a line of customers
waiting to pay a cashier. The queue has a head and a tail. When an element is en-
queued, it takes its place at the tail of the queue, just as a newly arriving customer
takes a place at the end of the line. The element dequeued is always the one at
the head of the queue, like the customer at the head of the line who has waited the
longest.

 
























/* WAP TO PERFORM QUEUE OPERATION ENQUEUE AND DEQUEUE */

# include<stdio.h>
# define MAX 5

int queue_arr[MAX];
int rear = -1;
int front = -1;

main()
{
int choice;
while(1)
{
printf("1.Insert\n");
printf("2.Delete\n");
printf("3.Display\n");
printf("4.Quit\n");
printf("Enter your choice : ");
scanf("%d",&choice);

switch(choice)
{
case 1 : insert();
            break;
case 2 : delete();
             break;
case 3: display();
            break;
case 4: exit(1);
default: printf("Wrong choice\n");
}/*End of switch*/
}/*End of while*/
}/*End of main()*/

insert()
{
int added_item;

if (rear==MAX-1)
printf("Queue Overflow\n");
else
{
if (front==-1) /*If queue is initially empty */
front=0;
printf("Input the element for adding in queue : ");
scanf("%d", &added_item);
rear=rear+1;
queue_arr[rear] = added_item ;
}
}/*End of insert()*/

delete()
{
if (front == -1 || front > rear)
{
printf("Queue Underflow\n");
return ;
}
else
{
printf("Element deleted from queue is : %d\n", queue_arr[front]);
front=front+1;
}
}/*End of del() */

display()
{
int i;
if (front == -1)
printf("Queue is empty\n");
else
{
printf("Queue is :\n");
for(i=front;i<= rear;i++)
printf("%d ",queue_arr[i]);
printf("\n");
}
}/*End of display() */

C LANGUAGE BOOK