用C语言创建一个双链表，用C语言代码描述

以下是用C语言实现双向链表的代码示例：

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

typedef struct node {
    int data;
    struct node *prev;
    struct node *next;
} Node;

Node *head = NULL;
Node *tail = NULL;

void insertAtBeginning(int value) {
    Node *new_node = (Node*) malloc(sizeof(Node));
    new_node->data = value;
    new_node->prev = NULL;
    new_node->next = head;
    if(head != NULL) {
        head->prev = new_node;
    } else {
        tail = new_node;
    }
    head = new_node;
}

void insertAtEnd(int value) {
    Node *new_node = (Node*) malloc(sizeof(Node));
    new_node->data = value;
    new_node->prev = tail;
    new_node->next = NULL;

    if(tail != NULL) {
        tail->next = new_node;
    } else {
        head = new_node;
    }
    tail = new_node;
}

void display() {
    Node *current = head;
    while(current != NULL) {
        printf("%d ",current->data);
        current = current->next;
    }
}

int main() {
    insertAtBeginning(10);
    insertAtEnd(20);
    insertAtBeginning(30);
    insertAtEnd(40);
    printf("Doubly linked list is: ");
    display();
    return 0;
}

这个示例代码创建了一个双向链表，实现了在链表头部和尾部插入元素，并能够遍历链表并输出其内容。