ds-lab-codes/CircQueue.c

#include<stdio.h>
#include<stdlib.h>

#define MALLOC(x,size,type) (x = (type*)malloc((size) * sizeof(type)))

typedef struct
{
    int n;
} element;

int front = 0, rear = 0, capacity;
element *queue;

void copy(element* start, element* end, element* newQueue)
{
    element* j;
    element* i;
    i = newQueue;
    j = start;
    for (; j < end; j++, i++)
    {
        *i = *j;
    }
}

void queueFull()
{
    element* newQueue;
    MALLOC(newQueue, capacity * 2, element);
    int start = (front + 1) % capacity;

    if (start < 2) // either 1 or 0, 1 when front at 0, 0 when front at capacity - 1
        copy(queue + start, queue + start + capacity - 1, newQueue);
    else
    {
        copy(queue + start, queue + capacity, newQueue);
        copy(queue, queue + rear + 1, newQueue + capacity - start);
    }

    front = 2 * capacity - 1;
    rear = capacity - 1;
    capacity *= 2;
    free(queue);
    queue = newQueue;
}

void addq(element item)
{
    rear = (rear + 1) % capacity;
    if (front == rear)
        queueFull();
    queue[rear] = item;
}

element deleteq()
{
    element item;
    if (front == rear)
    {
        item.n = -1;
        return item;
    }
    front = (front + 1) % capacity;
    return queue[front];
}

void displayq()
{
    int i;
    if (front == rear)
    {
        printf("Queue Empty\n");
        return;
    }
    for (i = (front + 1) % capacity; i != rear; i = (i + 1) % capacity)
        printf("%d\t", queue[i].n);
    printf("%d\n", queue[i].n);
    // printf("Front: %d Rear: %d\n", front, rear);
}

int main()
{
    int choice;
    element item;

    printf("Enter initial size: ");
    scanf("%d", &capacity);
    MALLOC(queue, capacity, element);

    while (1)
    {
        printf("\n1. Add\n2. Delete\n3. Display\n4. Exit\n");
        scanf("%d", &choice);

        switch (choice)
        {
        case 1:
            printf("Enter item to add: ");
            scanf("%d", &item.n);
            addq(item);
            break;

        case 2:
            item = deleteq();
            if (item.n == -1)
                printf("Queue Empty\n");
            else
                printf("Item deleted: %d\n", item.n);
            break;

        case 3:
            displayq();
            break;

        case 4:
            exit(0);

        default:
            printf("Invalid choice\n");
        }
    }

    return 0;
}