deque.c

/*  C Program to implement Deque using circular array  */

#include<stdio.h>
#include<stdlib.h>
#define MAX 7

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

void insert_frontEnd(int item);
void insert_rearEnd(int item);
int delete_frontEnd();
int delete_rearEnd();
void display();
int isEmpty();
int isFull();

int main()
{
        int choice,item;
        while(1)
        {
                printf("\n\n1.Insert at the front end\n");
                printf("2.Insert at the rear end\n");
                printf("3.Delete from front end\n");
                printf("4.Delete from rear end\n");
                printf("5.Display\n");
                printf("6.Quit\n");
                printf("\nEnter your choice : ");
                scanf("%d",&choice);

                switch(choice)
                {
                case 1:
                        printf("\nInput the element for adding in queue : ");
                        scanf("%d",&item);
                        insert_frontEnd(item);
                        break;
                case 2:
                        printf("\nInput the element for adding in queue : ");
                        scanf("%d",&item);
                        insert_rearEnd(item);
                        break;
                 case 3:
                        printf("\nElement deleted from front end is : %d\n",delete_frontEnd());
                        break;
                 case 4:
                        printf("\nElement deleted from rear end is : %d\n",delete_rearEnd());
                        break;
                 case 5:
                        display();
                        break;
                 case 6:
                        exit(1);
                 default:
                        printf("\nWrong choice\n");
                }/*End of switch*/
                printf("\nfront = %d, rear =%d\n", front , rear);
                display();
        }/*End of while*/
}/*End of main()*/

void insert_frontEnd(int item)
{
        if( isFull() )
        {
                printf("\nQueue Overflow\n");
                return;
        }
        if( front==-1 )/*If queue is initially empty*/
        {
                front=0;
                rear=0;
        }
        else if(front==0)
                front=MAX-1;
        else
                front=front-1;
        deque_arr[front]=item ;
}/*End of insert_frontEnd()*/

void insert_rearEnd(int item)
{
        if( isFull() )
        {
                printf("\nQueue Overflow\n");
                return;
        }
        if(front==-1)  /*if queue is initially empty*/
        {
                front=0;
                rear=0;
        }
        else if(rear==MAX-1)  /*rear is at last position of queue */
                rear=0;
        else
                rear=rear+1;
        deque_arr[rear]=item ;
}/*End of insert_rearEnd()*/

int delete_frontEnd()
{
        int item;
        if( isEmpty() )
        {
                printf("\nQueue Underflow\n");
                exit(1);
        }
        item=deque_arr[front];
        if(front==rear) /*Queue has only one element */
        {
                front=-1;
                rear=-1;
        }
        else
                if(front==MAX-1)
                        front=0;
                else
                        front=front+1;
        return item;
}/*End of delete_frontEnd()*/

int delete_rearEnd()
{
        int item;
        if( isEmpty() )
        {
                printf("\nQueue Underflow\n");
                exit(1);
        }
        item=deque_arr[rear];

        if(front==rear) /*queue has only one element*/
        {
                front=-1;
                rear=-1;
        }
        else if(rear==0)
                rear=MAX-1;
        else
                rear=rear-1;
        return item;
}/*End of delete_rearEnd() */

int isFull()
{
        if ( (front==0 && rear==MAX-1) || (front==rear+1) )
                return 1;
        else
                return 0;
}/*End of isFull()*/

int isEmpty()
{
        if( front == -1)
                return 1;
        else
                return 0;
}/*End of isEmpty()*/

void display()
{
        int i;
        if( isEmpty() )
        {
                printf("\nQueue is empty\n");
                return;
        }
        printf("\nQueue elements :\n");
        i=front;
        if( front<=rear )
        {
                while(i<=rear)
                        printf("%d ",deque_arr[i++]);
        }
        else
        {
                while(i<=MAX-1)
                        printf("%d ",deque_arr[i++]);
                i=0;
                while(i<=rear)
                        printf("%d ",deque_arr[i++]);
        }
        printf("\n");
}/*End of display() */