yaotti-queue.c

/* http://d.hatena.ne.jp/yaotti/20090330/1238391711 */

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




/* structure inside queue like atoms of a list */
typedef struct atom_t{
    int num;
    struct atom_t *next;
} atom_t;

/* queue structure */
typedef struct {
    struct atom_t *head;
    struct atom_t *tail;
} queue_t;




queue_t *newQ(void);
void deleteQ(queue_t *q);
void displayQ(queue_t *q);
void enqueue(queue_t *q, int i);
int dequeue(queue_t *q);




int main()
{
    queue_t *q = newQ();

    displayQ(q);
    enqueue(q, 1);
    displayQ(q);
    enqueue(q, 2);
    displayQ(q);
    enqueue(q, 3);
    displayQ(q);
    dequeue(q);
    displayQ(q);
    dequeue(q);
    displayQ(q);
    dequeue(q);
    displayQ(q);
    dequeue(q);
    displayQ(q);

    deleteQ(q);
    return 0;
}


queue_t *newQ(void)
{
    queue_t *q = (queue_t *)malloc(sizeof(queue_t));
    q->head = q->tail = NULL;
    return q;
}

void deleteQ(queue_t *q)
{
    atom_t *a = q->head;
    atom_t *n = q->head;

    while (a != NULL) {
	n = a->next;
	free(a);
	a = n;
    }
    free(q);
}


void displayQ(queue_t *q)
{
    atom_t *a = q->head;

    printf("[ ");
    while (a != NULL) {
        printf("%d ", a->num);
        a = a->next;
    }
    printf("]\n");
}


void enqueue(queue_t *q, int i)
{
    atom_t *a = (atom_t *)malloc(sizeof(atom_t));
    a->num = i;
    a->next = NULL;

    if (q->tail == NULL) {
	q->head = q->tail = a;
    } else {
	q->tail->next = a;
	q->tail = a;
    }
}


int dequeue(queue_t *q)
{
    int v;
    atom_t* a = q->head;

    if (a != NULL) {
	v = a->num;
	q->head = a->next;
	free(a);
    } else {
	v = 0;
    }
    return v;
}