通过数组实现队列

#include <stdio.h>
#define MAX_SIZE 101  // 存储队列的数组的最大大小

typedef struct    //定义一个Queue的结构体
{
	int A[MAX_SIZE];
	int front, rear;
} Queue;

//初始化队列
void init(Queue* q)
{
	q->front = -1;
	q->rear = -1;
}

//判断队列是否为空
int IsEmpty(Queue* q)
{
	if (q->front == -1 && q->rear == -1)
		return 1;
	return 0;
}

//判断队列是否是满
int IsFull(Queue* q)
{
	if ((q->rear + 1) % MAX_SIZE == q->front)  //循环数组，下一个是（i+1）%N
		return 1;
	return 0;
}

//入队
void enqueue(Queue* q, int x)
{
	printf("入队元素：%d\n", x);
	if (IsFull(q))
	{
		printf("队列已满，无法入队！\n");
		return;
	}
	if (IsEmpty(q))
	{
		q->front = q->rear = 0;
	}
	else
	{
		q->rear = (q->rear + 1) % MAX_SIZE;  //指向下一个
	}

	q->A[q->rear] = x;
}

//出队
void dequeue(Queue* q)
{
	printf("出队元素：\n");
	if (IsEmpty(q))
	{
		printf("队列为空，无法出队");
		return;
	}
	else if (q->front == q->rear)
	{
		q->front = q->rear = -1;
	}
	else
	{
		q->front = (q->front + 1) % MAX_SIZE;  //指向下一节点
	}
}

//返回头元素
int front(Queue* q)
{
	if (q->front == -1)
	{
		printf("错误：空队列无法返回队头元素\n");
		return -1;
	}
	return q->A[q->front];
}
 
//输出队列元素
void printQueue(Queue* q)
{
	int count = (q->rear + MAX_SIZE - q->front) % MAX_SIZE + 1;
	printf("队列：");
	for (int i = 0; i < count; i++)
	{
		int index = (q->front + i) % MAX_SIZE;
		printf("%d", q ->A[index]);
	}

	printf("\n\n");
}
int main() {
	/* 测试队列的实现，每次入队或出队后打印队列中的元素 */
	Queue q;
	init(&q);
	enqueue(&q, 2);
	printQueue(&q);
	enqueue(&q, 4);
	printQueue(&q);
	enqueue(&q, 6);
	printQueue(&q);
	dequeue(&q);
	printQueue(&q);
	enqueue(&q, 8);
	printQueue(&q);
	return 0;
}

用链表实现队列

#include <stdio.h>
#include <stdlib.h>
struct Node {   //定义一个节点
	int data;
	struct Node* next;
}; 
struct Node* front = NULL;  //定义开头指针
struct Node* rear = NULL;   //定义末尾指针

//入队
void Enquene(int x)
{
	struct Node* temp = (struct Node*)malloc(sizeof(struct Node));  //动态分配内存空间
	temp->data = x;
	temp->next = NULL;

	if (front == NULL && rear == NULL)  //当头尾节点都为空，指向temp，并返回
	{
		front = rear = temp;  
		return;
	}
	rear->next = temp;   //首尾不为空，尾节点指向temp
	rear = temp;
}

//出队
void Dequene()
{
	struct Node* temp = front; //定义temp指针，保存front所指向的节点

	if (front == NULL) return;
	if (front == rear)  //特殊情况
	{
		front = rear = NULL;
	}
	else    //正常情况
	{
		front = front->next;  
	}
	free(temp);  //释放temp先前保存的front的指针
}
void Print() //迭代正序打印链表  与单链表相同
{
	struct Node* temp = front;
	printf("正序列表是：");
	while (temp != NULL)  //遍历链表
	{
		printf("%d", temp->data);
		temp = temp->next;  //往下走
	}
	printf("\n");

}
int main()
{
	Enquene(2);
	Print();
	Enquene(3);
	Print();

	Dequene();
	Print();
}