栈基本操作的实现（链式栈）

学习完链表后再学习栈，不难发现栈其实是一个简化版的链表。由于其“First in,last out(先进后出，FILO)”的特性，就决定了我们只能在栈顶对栈进行压栈和出栈操作。

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

typedef struct Node
{
	int data;
	struct Node * pNext;
}NODE, * PNODE;

typedef struct Stack
{
	PNODE pTop;
	PNODE pBottom;
}STACK, * PSTACK;  //PSTACK 等价于 struct STACK *

//初始化一个栈
void init(PSTACK pS)
{
	pS->pTop = (PNODE)malloc(sizeof(NODE));
	if (NULL == pS->pTop)
	{
		printf("动态内存分配失败!\n");
		exit(-1);
	}
	else
	{
		pS->pBottom = pS->pTop;
		pS->pTop->pNext = NULL; //pS->Bottom->pNext = NULL;
	}
}

//压栈（入栈）
void push(PSTACK pS, int val)
{
	PNODE pNew = (PNODE)malloc(sizeof(NODE));
	if (NULL == pNew)
	{
		printf("动态内存分配失败!\n");
		exit(-1);
	}
	pNew->data = val;
	pNew->pNext = pS->pTop; //pS->Top不能改成pS->Bottom
	pS->pTop = pNew;

	return;
}

//遍历
void traverse(PSTACK pS)
{
	PNODE p = pS->pTop;

	while (p != pS->pBottom)
	{
		printf("%d  ", p->data);
		p = p->pNext;
	}
	printf("\n");

	return;
}

//判断栈是否为空
bool isEmpty(PSTACK pS)
{
	if (pS->pTop == pS->pBottom)
		return true;
	else
		return false;
}

//把pS所指向的栈出栈一次，并把出栈的元素存入pVal形参所指向的变量中，如果出栈失败，返回false,否则返回true
bool pop(PSTACK pS, int * pVal)
{
	if ( isEmpty(pS) ) //pS本身存放的就是S的地址
	{
		return false;
	}
	else
	{
		PNODE r = pS->pTop;
		*pVal = r->data;
		pS->pTop = r->pNext;
		free(r);
		r = NULL;

		return true;
	}
}

//栈的清空
void clear(PSTACK pS)
{
	if ( isEmpty(pS) )
	{
		return;
	}
	else
	{
		PNODE p = pS->pTop;
		PNODE q = NULL;

		while (p != pS->pBottom)
		{
			q = p->pNext;
			free(p);
			p = q;
		}
		pS->pTop = pS->pBottom;
	}
}