栈的相关操作

# include <stdio.h>
# include <malloc.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 *

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
    
    clear(&S);
    //traverse(&S); //遍历输出

    if ( pop(&S, &val) )
    {
        printf("出栈成功，出栈的元素是%d
", val);
    }
    else
    {
        printf("出栈失败!
");
    }

    traverse(&S); //遍历输出

    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!
");
        exit(-1);
    }
    else
    {
        pS->pBottom = pS->pTop;
        pS->pTop->pNext = NULL; //pS->Bottom->pNext = NULL;
    }
}

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->Bottom
    pS->pTop = pNew;

    return;
}

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

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

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