线性结构的应用--栈的简单实现

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

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

typedef struct Stack
{
    PNODE pTop;  //指向顶端元素
    PNODE pBottom; //指向底部元素（头节点 ，不是第一个有效元素）
} STACK , * PSTACK;

void init(PSTACK pS)
{
    pS ->pTop == (PNODE)malloc(sizeof(NODE)); //使pTop指向空链表的头节点
    if(NULL ==  pS->pTop)
    {
        printf("分配内存失败");
        exit(-1);
    }
    else
    {
         pS->pBottom = pS ->pTop                //使pBottom指向空链表的头节点
         pS ->pTop->pNext = null;               //清空头节点的指针域
    }
    
}
void traverse（PSTACK pS）
{
    PNODE p = pS ->pTop;
    while(p!=pS->pBottom)
    {
        printf("%d" , p->data);
        p=p->pNext;
    }
    return;
}

bool empty(PSTACK pS)
{
    if(pS->oTop ==pS ->pBottom)
    {
        return true;
    }
    else
    {
        return false;
    }
}

void pop (PSTACK pS ,int * pVal)
{
    if(empty(pS))
    {
        return false;
    }
    else
    {
        PNODE r = pS ->pTop;  //把出栈元素 赋值临时节点
        &pVal = r ->data;
        pS->pTop = r ->pNext;    //把下个元素赋值给 TOP
        free(r);
        r= NULL;
        return true;
    }
}

//清空数据
void clear(PSTACK pS)
{
    if(empty(pS))
    {
        return false;
    }
    else
    {
        PNODE p = pS->pTop;   
        PNODE q = NULL;   //一下指向要释放的元素的指针域的值
        while(p!=pS->pBottom)
        {
            q = p->pNext;
            free(p);
            p=q;
        }
        pS ->pTop = pS ->pBottom;
    }
}

//增加
void push(PSTACK pS, int val)
{
    PNODE pNew = (PNODE)malloc(sizeof(NODE));  //给val分配新的节点
    pNew->data = val ;
    pNew -> pNext = pS->pTop;            //新的节点指针域指向栈顶
    pS->pTop = pNew;                     //pTop指向最新的节点
}
int main (void)
{
    int val;
    STACK S;  //STACK 等价于struct Stack
    init(&S); //初始化
    push(&S , 1);//压栈
    pop (S ,&val);
    traverse(); //遍历输出
    
}