QLS

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

typedef struct node{
    int data;
    struct node *next;
    struct node *pre;
}node;

typedef struct {
    node *head;
    node *tail;
}Queue;

void intiallize (Queue *q){
    q->head = q->tail = NULL;
}

int isempty(Queue *q){
    return q->head==NULL;
}

void add_in_front(Queue *q, int x){
    node *p = (node*) malloc(sizeof(node));
    if (!isempty(q)){
        p->data = x;
        p->next = q->head;
        p->pre = NULL;
       (q->tail)->next=p;
    }else{
        p->data = x;
        p->next = NULL;
        p->pre = NULL;
        (q->tail)->next=p;
    }
}



int main()
{
    Queue q; intiallize(&q);
    printf("Hello world!\n");
    return 0;
}