一、什么是栈

栈是一种特殊的线性表，只允许在固定的一端进行插入和删除操作。进行插入和删除的一段叫做栈顶，另一段叫做栈底

压栈：插入数据
出栈：删除数据
压栈和出栈都是在栈顶

二、栈的实现

栈的实现分为两种方式，用数组或者链表实现，相较于链表而言，数组实现尾插的代价更小，所以我们用数组实现

三、实现栈所需的函数

• 1.栈的初始化

void StackInit(ST* ps)
{
	assert(ps);
	ps->a = NULL;
	ps->capacity = ps->top = 0;

}

• 2.栈的销毁

void StackDestroy(ST* ps)
{
	assert(ps);
	free(ps->a);
	ps->a = NULL;
	ps->capacity = ps->top = 0;
}

• 3.栈的插入

void StackPush(ST* ps, STDataType x)
{
	assert(ps);
	if (ps->capacity == ps->top)
	{
		int newcapacity = ps->capacity == 0 ? 4 : ps->capacity * 2;
		STDataType* tmp = (STDataType*)realloc(ps->a, sizeof(STDataType)*newcapacity);
		if (tmp == NULL)
		{
			perror("realloc fail");
			return;
		}
		ps->a = tmp;
		ps->capacity = newcapacity;
	}
		ps->a[ps->top] = x;
		ps->top++;
}

插入的时候我们首先要考虑容量是否够，这里与top比较一下，如果刚好相等，我们可以realloc二倍扩容，扩容好了之后top就要+！

• 4.栈元素的删除

void StackPop(ST* ps)
{
	assert(ps);
	assert(ps->a);
	ps->top--;
}

这里直接让top-1，下次如果想要插入的话直接可以把之前top元素覆盖

• 5.取栈顶元素

STDataType StackTop(ST* ps)
{
	assert(ps);
	assert(ps->a);
	return ps->a[ps->top - 1];

}

• 6.栈中元素的个数

int StackSize(ST* ps)
{
	assert(ps);
	return ps->top;
}

• 7.栈元素是否为空的判断

bool StackEmpty(ST* ps)
{
	return ps->top==0;
}

四、完整栈的展现

#pragma once
#include<stdio.h>
#include<assert.h>
#include<stdlib.h>
#include<stdbool.h>

typedef int QDataType;

typedef struct QueueNode
{
	int val;
	struct QueueNode* next;
}QueueNode;


typedef struct Queue
{
	QueueNode* phead;
	QueueNode* ptail;
	int size;
}Queue;



void QueueInit(Queue* pq);

void QueueDestroy(Queue* pq);

void QueuePush(Queue* pq, QDataType x);

void QueuePop(Queue* pq);

QDataType QueueFront(Queue* pq);

QDataType QueueBack(Queue* pq);

bool QueueEmpty(Queue* pq);

int QueueSize(Queue* pq);

#define _CRT_SECURE_NO_WARNINGS 1
#include"stack.h"


void StackInit(ST* ps)
{
	assert(ps);
	ps->a = NULL;
	ps->capacity = ps->top = 0;

}

void StackDestroy(ST* ps)
{
	assert(ps);
	free(ps->a);
	ps->a = NULL;
	ps->capacity = ps->top = 0;
}

void StackPush(ST* ps, STDataType x)
{
	assert(ps);
	if (ps->capacity == ps->top)
	{
		int newcapacity = ps->capacity == 0 ? 4 : ps->capacity * 2;
		STDataType* tmp = (STDataType*)realloc(ps->a, sizeof(STDataType)*newcapacity);
		if (tmp == NULL)
		{
			perror("realloc fail");
			return;
		}
		ps->a = tmp;
		ps->capacity = newcapacity;
	}
		ps->a[ps->top] = x;
		ps->top++;
}

void StackPop(ST* ps)
{
	assert(ps);
	assert(ps->a);
	ps->top--;
}


STDataType StackTop(ST* ps)
{
	assert(ps);
	assert(ps->a);
	return ps->a[ps->top - 1];

}

int StackSize(ST* ps)
{
	assert(ps);
	return ps->top;
}

bool StackEmpty(ST* ps)
{
	return ps->top==0;
}

#define _CRT_SECURE_NO_WARNINGS 1
#include"stack.h"

int main()
{
	ST p;
	StackInit(&p);
	StackPush(&p, 1);
	StackPush(&p, 2);
	StackPush(&p, 3);
	StackPush(&p, 4);
	StackPush(&p, 5);
	StackPush(&p, 6);
	StackPush(&p, 7);
	while (!StackEmpty(&p))
	{
		printf("%d ", StackTop(&p));
		StackPop(&p);
	}
	return 0;
}

五、栈的思维导图