队列的数组实现

typedef int ElementType;

#ifndef _Queue_h
#define _Queue_h

struct QueueRecord;
typedef struct QueueRecord *Queue;

int isEmpty(Queue q);
int isFull(Queue q);
Queue createQueue(int maxElements);
void disposeQueue(Queue q);
void makeEmpty(Queue q);
void enqueue(ElementType X, Queue q);
ElementType front(Queue q);
void dequeue(Queue q);
ElementType frontAndDequeue(Queue q);

#endif

#include"queue.h"
#include"fatal.h"
#include<stdlib.h>

#define	MinQueueSize (5)

struct QueueRecord{
int capacity;
int front;
int rear;
int size;
ElementType *array;
};

int isEmpty(Queue q) {
return q->size == 0;
}

int isFull(Queue q) {
return q->size == q->capacity;
}

Queue createQueue(int maxElements) {
if (maxElements < MinQueueSize)
Error("Queue size is too small");
Queue q = malloc(sizeof(struct QueueRecord));
if (q == NULL)
Error("out of memory");
q->array = malloc(maxElements*sizeof(ElementType));
if(q->array==NULL)
Error("out of memory");
q->capacity = maxElements;
makeEmpty(q);
return q;
}

void makeEmpty(Queue q) {
q->size = 0;
q->front = 1;//这个是重点啊，当增加一个元素之后，rear和front同时都是1
q->rear = 0;
}

void enqueue(ElementType X, Queue q) {
if (isFull(q))
Error("queue is full");
q->size++;
q->rear = (q->rear + 1) % q->capacity;
q->array[q->rear] = X;
}

ElementType front(Queue q) {
if (isEmpty(q))
Error("queue is empty");
return q->array[q->front];
}

void dequeue(Queue q) {
if (isEmpty(q))
Error("queue is empty");
q->size--;
q->front = (q->front + 1) % q->capacity;
}

ElementType frontAndDequeue(Queue q) {
ElementType x = front(q);
dequeue(q);
return x;
}

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

int main() {
Queue q = createQueue(50);
for (int i = 0; i < 8; i++){
enqueue(i, q);
}
printf("%d\n", frontAndDequeue(q));
printf("%d\n", frontAndDequeue(q));
printf("%d\n", frontAndDequeue(q));
}