Topic: Circular Queues

Difficulty: Medium

Year(Marks): May2018(10 mks)

    #include <stdio.h>
    #define size 5

    void insertq(int[], int);
    void deleteq(int[]);
    void display(int[]);

    int front =  - 1;
    int rear =  - 1;

    int main()
    {
        int n, ch;
        int queue[size];
        do
        {
            printf("\n\n Circular Queue:\n1. Insert \n2. Delete\n3. Display\n0. Exit");
            printf("\nEnter Choice 0-3? : ");
            scanf("%d", &ch);
            switch (ch)
            {
                case 1:
                    printf("\nEnter number: ");
                    scanf("%d", &n);
                    insertq(queue, n);
                    break;
                case 2:
                    deleteq(queue);
                    break;
                case 3:
                    display(queue);
                    break;
            }
        }while (ch != 0);
    }


    void insertq(int queue[], int item)
    {
        if ((front == 0 && rear == size - 1) || (front == rear + 1))
        {
            printf("queue is full");
            return;
        }
        else if (rear ==  - 1)
        {
            rear++;
            front++;
        }
        else if (rear == size - 1 && front > 0)
        {
            rear = 0;
        }
        else
        {
            rear++;
        }
        queue[rear] = item;
    }

    void display(int queue[])
    {
        int i;
        printf("\n");
        if (front > rear)
        {
            for (i = front; i < size; i++)
            {
                printf("%d ", queue[i]);
            }
            for (i = 0; i <= rear; i++)
                printf("%d ", queue[i]);
        }
        else
        {
            for (i = front; i <= rear; i++)
                printf("%d ", queue[i]);
        }
    }

    void deleteq(int queue[])
    {
        if (front ==  - 1)
        {
            printf("Queue is empty ");
        }
        else if (front == rear)
        {
            printf("\n %d deleted", queue[front]);
            front =  - 1;
            rear =  - 1;
        }
        else
        {
            printf("\n %d deleted", queue[front]);
            front++;
        }
    }