栈程序算法

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

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

typedef struct stack
{
    PNODE pTop;
    PNODE pBottom;
}STACK, *PSTACK;

void init(PSTACK);
void push(PSTACK, int );
void traverse(PSTACK);
bool empty(PSTACK);
bool pop(PSTACK, int *);
void clear(PSTACK); //清楚里面的内容，框架还存在

int main()
{
    STACK S; //STACK等价于 struct Stack
    int val;

    init(&S); //目的是建立一个空栈
   push(&S, 1); //压栈
    push(&S, 2);
    push(&S, 3);
    traverse(&S); //遍历输出
    if(pop(&S,&val))
        printf("出栈成功，出栈的元素为: %d \n", val);
    else
        printf("出栈失败！\n");
    traverse(&S); //遍历输出
    clear(&S);
    traverse(&S); //遍历输出

    return 0;
}
void init(PSTACK pS)
{
    pS->pTop = (PNODE)malloc(sizeof(NODE));
    if(pS->pTop==NULL)
    {
        printf("动态内存分配失败!\n");
        exit(-1);
    }
    else
    {
        pS->pBottom = pS->pTop; //不能写pS->pTop = pS->pBottom
        pS->pTop->next = NULL; //等价于pS->pBottom->next = NULL;
    }
    //return;
}
void push(PSTACK pS, int val)
{
    PNODE pNew = (PNODE)malloc(sizeof(NODE));

    pNew->data = val;
    pNew->next = pS->pTop; //pS->pTop不能换成pS->pBottom
    pS->pTop = pNew;
    return;
}
void traverse(PSTACK pS)
{
    PNODE p = pS->pTop; //建一个遍历指针
    while(p!=pS->pBottom)
    {
        printf("%d ",p->data);
        p = p->next;
    }
    printf("\n");
    return;
}
bool empty(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(empty(pS)) //pS本身存放的就是S的地址
    {
        return false; //栈空的时候出栈失败
    }
    else
    {
        PNODE r = pS->pTop; //创建一个指针用来指向出栈的元素
        *pVal = r->data; //用pval存放出栈的元素
        pS->pTop = r->next;
        free(r);
        r = NULL;
    }
    return true;
}
void clear(PSTACK pS)
{
    PNODE p = pS->pTop;
    PNODE q = NULL;
    while(p!=pS->pBottom)
    {
        q = p->next; //q用于存放p的后继，以防free（p）找不到p的后继
        free(p);
        p = q;
    }
    pS->pTop = pS->pBottom;
    return;
}