C program for array implementation of queue




#include <stdio.h>

#include <stdlib.h>

#include <limits.h>

 

// A structure to represent a queue

struct Queue

{

    int front, rear, size;

    unsigned capacity;

    int* array;

};

 

// function to create a queue of given capacity. It initializes size of

// queue as 0

struct Queue* createQueue(unsigned capacity)

{

    struct Queue* queue = (struct Queue*) malloc(sizeof(struct Queue));

    queue->capacity = capacity;

    queue->front = queue->size = 0;

    queue->rear = capacity - 1;  // This is important, see the enqueue

    queue->array = (int*) malloc(queue->capacity * sizeof(int));

    return queue;

}

 

// Queue is full when size becomes equal to the capacity

int isFull(struct Queue* queue)

{  return (queue->size == queue->capacity);  }

 

// Queue is empty when size is 0

int isEmpty(struct Queue* queue)

{  return (queue->size == 0); }

 

// Function to add an item to the queue.  It changes rear and size

void enqueue(struct Queue* queue, int item)

{

    if (isFull(queue))

        return;

    queue->rear = (queue->rear + 1)%queue->capacity;

    queue->array[queue->rear] = item;

    queue->size = queue->size + 1;

    printf("%d enqueued to queue\n", item);

}

 

// Function to remove an item from queue.  It changes front and size

int dequeue(struct Queue* queue)

{

    if (isEmpty(queue))

        return INT_MIN;

    int item = queue->array[queue->front];

    queue->front = (queue->front + 1)%queue->capacity;

    queue->size = queue->size - 1;

    return item;

}

 

// Function to get front of queue

int front(struct Queue* queue)

{

    if (isEmpty(queue))

        return INT_MIN;

    return queue->array[queue->front];

}

 

// Function to get rear of queue

int rear(struct Queue* queue)

{

    if (isEmpty(queue))

        return INT_MIN;

    return queue->array[queue->rear];

}

 

// Driver program to test above functions./

int main()

{

    struct Queue* queue = createQueue(1000);

 

    enqueue(queue, 10);

    enqueue(queue, 20);

    enqueue(queue, 30);

    enqueue(queue, 40);

 

    printf("%d dequeued from queue\n", dequeue(queue));

 

    printf("Front item is %d\n", front(queue));

    printf("Rear item is %d\n", rear(queue));

 

    return 0;

}

Output:

10 enqueued to queue
20 enqueued to queue
30 enqueued to queue
40 enqueued to queue
10 dequeued from queue
Front item is 20
Rear item is 40