题解 | #【模板】栈#

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

typedef struct StackNode {
    int x;
    struct StackNode* next;
} StackNode;

typedef StackNode* LinkStack;

void StackInit(LinkStack *s);
void Distop(LinkStack *s);
void RemovePop(LinkStack *s);
void PushTop(LinkStack *s, int x);

int main() {
    int n, x;
    LinkStack s = NULL;
    char str[5];
    
    scanf("%d", &n);
    StackInit(&s);
    
    for (int i = 0; i < n; i++) {
        scanf("%s %d", str, &x); // 注意这里使用 &x
        if (strcmp(str, "pop") == 0) {
            RemovePop(&s);
        } else if (strcmp(str, "top") == 0) {
            Distop(&s);
        } else {
            PushTop(&s, x);
        }
    }
    
    return 0;
}

void StackInit(LinkStack *s){
    *s = NULL;
}

void Distop(LinkStack *s) {
    if (*s == NULL) {
        printf("error\n");
    } else {
        printf("%d\n", (*s)->x);
    }
    return;
}

void RemovePop(LinkStack *s) {
    if (*s == NULL) {
        printf("error\n");
    } else {
        printf("%d\n",(*s)->x);
        LinkStack p = *s;
        *s = (*s)->next;
        free(p);
        p = NULL; // 释放后将指针设置为 NULL 避免悬挂指针
    }
    return;
}

void PushTop(LinkStack *s, int y){
    LinkStack newnode = (LinkStack)malloc(sizeof(StackNode));
    newnode->x = y;
    newnode->next = *s;
    *s = newnode;
}