数据结构初学————栈的基本操作

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

void init(PSTACK);
void push(PSTACK, int); 
void traverse(PSTACK);
bool pop(PSTACK, int *); 
void clear(PSTACK pS);

int main(void)
{ 
	STACK S;//STACK  等价于 struct Stack;
    int val;
	 
	init( &S);//目的是造出一个空栈 
	push(&S, 1);//压栈 
	push(&S, 2);
	push(&S, 3);
	push(&S, 4);
	push(&S, 5);
	push(&S, 6);
	traverse(&S); //遍历输出 
	
	if( pop(&S, &val) )//出栈
	{
		printf("出栈成功，出栈的元素是%d\n ", val);
	}
	else
	{
		printf("出栈失败！\n");
	}
	
	traverse(&S);
	clear(&S);
	traverse(&S);
	if( pop(&S, &val) )//出栈
	{
		printf("出栈成功，出栈的元素是%d\n ", val);
	}
	else
	{
		printf("出栈失败！\n");
	}
		 
	return 0;
}

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->pBottom->pNext = NULL;
	} 
	return;
}

void push(PSTACK pS, int val)
{
	PNODE pNew = (PNODE)malloc(sizeof(NODE));
	pNew->data = val;
	pNew->pNext = pS->pTop; //pS.Top 不能改成pS.pBottom;
	pS->pTop = pNew; 
	return;
}

void traverse(PSTACK pS)
{
	PNODE p = pS->pTop;
	
	while(p != pS->pBottom)
	{
		printf("%d ", p->data);
		p = p->pNext;
	}
	printf("\n");
	return;
}

bool empty(PSTACK pS) 
{
	if(pS->pBottom == pS->pTop) 
		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(empty(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;
	}
} 

//clear清空
void clear(PSTACK pS)
{
	if(empty(pS))
	{
		return;
	}
	else
	{
		PNODE p = pS->pTop;
		PNODE q = NULL;
		while(pS ->pBottom != p)
		{
			q = p ->pNext;
			free(p);
			p = q;
		}
		pS ->pTop = pS->pBottom;
	}
}