线性结构的常见应用之一 栈

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

//先定义结点类型
typedef struct Node {
    int data;
    struct Node * pNext;
} NODE,*PNODE;

//定义一个栈

typedef struct Stack {
    PNODE pTop;
    PNODE pBottom;
} STATCK,*PSTACK;
//初始化一个栈
void init(PSTACK pS);
//遍历一个栈
void traverse(PSTACK pS);
//压栈
void push(PSTACK pS,int val);
//出栈
bool pop(PSTACK pS,int *val);
//clear
void clear(PSTACK pS);

int main(void) {
    STATCK S;
    int val;
    init(&S);
    push(&S,3);
    push(&S,4);
    push(&S,7);
    push(&S,9);
    traverse(&S);

    if(pop(&S,&val)) {
        printf("出栈的值是%d!\n",val);
    } else {
        printf("出栈失败!\n");
    }
    traverse(&S);
    clear(&S);//清空栈
    traverse(&S);//清空成功

    return 0;
}

//初始化栈
//初始化的目的就是将pTop和pBottom两个指针指向同一个没有实际意义的头结点这样就实现了栈的初始化
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;
    }
}
//遍历一个栈
void traverse(PSTACK pS) {
    PNODE p = pS->pTop;
    while(p!=pS->pBottom) {
        printf("%d   ",p->data);
        p = p->pNext;
    }
    printf("\n");
    return;
}
//压栈
void push(PSTACK pS,int val) {
    PNODE pNew = (PNODE)malloc(sizeof(NODE));
    if(NULL == pNew->pNext) {
        printf("动态内存分配失败!\n");
        exit(-1);
    }
    pNew->pNext = NULL;
    pNew->data = val;
    pNew->pNext = pS->pTop;
    pS->pTop = pNew;
    return;
}
bool empty(PSTACK pS) {
    if(pS->pTop == pS->pBottom) {
        return true;
    } else {
        return false;
    }
}
bool pop(PSTACK pS,int *val) {
    if(empty(pS)) {
        printf("栈为空\n");
        return false;
    } else {
        PNODE p = pS->pTop;
        *val = p->data;
        pS->pTop = p->pNext;
        free(p);
        p = NULL;
        return true;
    }
}

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