使用数组实现双头队列，参考结构： typedef struct Deque{ Type *array; //数组 int ihead; //头索引 int itail; //尾索引 int entry_count; // 现存数据数量 int array_capacity; // 容量大小 }Deque, *Deque_link;

下面是使用数组实现双头队列的代码示例：

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

#define Type int  // 定义元素类型

typedef struct Deque{
    Type *array;         // 数组
    int ihead;           // 头索引
    int itail;           // 尾索引
    int entry_count;     // 现存数据数量
    int array_capacity;  // 容量大小
}Deque, *Deque_link;

// 初始化双头队列
void init_deque(Deque_link deque, int capacity) {
    deque->array = (Type*)malloc(sizeof(Type) * capacity);
    deque->ihead = 0;
    deque->itail = capacity - 1;
    deque->entry_count = 0;
    deque->array_capacity = capacity;
}

// 判断队列是否为空
int is_empty(Deque_link deque) {
    return deque->entry_count == 0;
}

// 判断队列是否已满
int is_full(Deque_link deque) {
    return deque->entry_count == deque->array_capacity;
}

// 获取队列长度
int size(Deque_link deque) {
    return deque->entry_count;
}

// 从队头入队
void push_front(Deque_link deque, Type value) {
    if (is_full(deque)) {
        printf("Deque is full, cannot push_front!\n");
        return;
    }
    deque->array[deque->ihead] = value;
    deque->ihead = (deque->ihead + 1) % deque->array_capacity;
    deque->entry_count++;
}

// 从队尾入队
void push_back(Deque_link deque, Type value) {
    if (is_full(deque)) {
        printf("Deque is full, cannot push_back!\n");
        return;
    }
    deque->array[deque->itail] = value;
    deque->itail = (deque->itail - 1 + deque->array_capacity) % deque->array_capacity;
    deque->entry_count++;
}

// 从队头出队
Type pop_front(Deque_link deque) {
    if (is_empty(deque)) {
        printf("Deque is empty, cannot pop_front!\n");
        return -1;
    }
    Type value = deque->array[(deque->ihead - 1 + deque->array_capacity) % deque->array_capacity];
    deque->ihead = (deque->ihead - 1 + deque->array_capacity) % deque->array_capacity;
    deque->entry_count--;
    return value;
}

// 从队尾出队
Type pop_back(Deque_link deque) {
    if (is_empty(deque)) {
        printf("Deque is empty, cannot pop_back!\n");
        return -1;
    }
    Type value = deque->array[(deque->itail + 1) % deque->array_capacity];
    deque->itail = (deque->itail + 1) % deque->array_capacity;
    deque->entry_count--;
    return value;
}

int main() {
    Deque deque;
    int capacity = 10;
    init_deque(&deque, capacity);

    // 从队头入队
    for (int i = 0; i < 5; i++) {
        push_front(&deque, i);
    }

    // 从队尾入队
    for (int i = 5; i < 10; i++) {
        push_back(&deque, i);
    }

    // 从队头出队
    while (!is_empty(&deque)) {
        printf("%d ", pop_front(&deque));
    }
    printf("\n");

    // 从队尾出队
    for (int i = 0; i < 5; i++) {
        push_front(&deque, i);
    }
    while (!is_empty(&deque)) {
        printf("%d ", pop_back(&deque));
    }
    printf("\n");

    return 0;
}

在上面的代码中，我们使用了一个数组来存储双头队列中的元素。`ihead` 表示队头的位置，`itail` 表示队尾的位置，`entry_count` 表示队列中现存的元素数量，`array_capacity` 表示数组的容量大小。在初始化双头队列时，我们先动态分配一个数组，并将队头和队尾的位置分别初始化为 0 和 `capacity - 1`。当队列满时，我们无法继续插入元素，当队列为空时，我们无法出队元素。