线性循环队列

队列是先进先出，和栈相反.

线性循环队列，牺牲一个空间，实现循环。比如空间大小为4，牺牲一个空间，所以最多放3个元素。

假设front指向0位置，tail指向3位置

出队后

front指向1位置，tail位置不变还是3

入队后（4）

front指向不变还是1，tail指向0位置

出队后

front指向2位置，tail位置不变还是0

入队后（5）

front指向不变还是2，tail指向1位置

whilequeue.h

#ifndef __WHILEQUEUE__
#define __WHILEQUEUE__#include <stdio.h>
#include <malloc.h>
#include <assert.h>
#include <memory.h>
#include <stdbool.h>#define WHILEQUEUE_INIT_SIZE 8typedef int ElemType;typedef struct whilequeue{ElemType* base;int front;int tail;
}whilequeue;void init(whilequeue*);
//入队
void enQueue(whilequeue*, ElemType);
void show_list(whilequeue*);
//出队
void deQueue(whilequeue*);
void clear(whilequeue*);
void destroy(whilequeue*);
#endif

whilequeue.c

#include "whilequeue.h"void init(whilequeue* seq){seq->base = (ElemType*)malloc(sizeof(ElemType) * WHILEQUEUE_INIT_SIZE);seq->front = seq->tail = 0;
}
void enQueue(whilequeue* seq, ElemType x){//判断队列是否已满if((seq->tail + 1) % WHILEQUEUE_INIT_SIZE == seq->front){printf("queue is full\n");return;}seq->base[seq->tail] = x;seq->tail = (seq->tail + 1) % WHILEQUEUE_INIT_SIZE;
}
void show_list(whilequeue* seq){int i = seq->front;while(i != seq->tail){printf("%d\n", seq->base[i++ % WHILEQUEUE_INIT_SIZE]);i = i % WHILEQUEUE_INIT_SIZE;}
}
void deQueue(whilequeue* seq){//判断队列是否为空，空了的话，就不需要移动frontif(seq->front == seq->tail)return;seq->front = (seq->front + 1) % WHILEQUEUE_INIT_SIZE;
}
void clear(whilequeue* seq){}
void destroy(whilequeue* seq){}

whilequeuemain.c

#include "whilequeue.h"int main(){whilequeue list;init(&list);int select = 1;ElemType item;int index;while(select){printf("*****************************************\n");printf("*** [1]   push        [2]  pop        ***\n");printf("*** [3]   show_list   [4]  length     ***\n");printf("*** [5]   clear       [6]  destroy    ***\n");printf("*** [0]   quit                        ***\n");printf("*****************************************\n");printf("请选择:>");scanf("%d", &select);if(0 == select)break;switch(select){case 1:printf("请输入要插入的数据>\n");scanf("%d",&item);enQueue(&list, item);show_list(&list);break;case 2:deQueue(&list);show_list(&list);break;case 3:show_list(&list);break;case 5:clear(&list);show_list(&list);break;case 6:destroy(&list);break;default:printf("输入的选择错误，请重新选择\n");break;}}//destroy(&list);
}