题解 | 【模板】栈的操作

自定义栈实现：

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

typedef struct stack {
    int val;
    struct stack* top;
} stack;

stack* top = NULL;
int capacity = 0;

void push(int x) {
    stack* newNode = malloc(sizeof(stack));
    newNode->val = x;
    newNode->top = top;
    top = newNode;
    ++capacity;
}

void pop() {
    if (capacity) {
        stack* curTop = top;
        top = curTop->top;
        free(curTop);
        --capacity;
    } else {
        puts("Empty");
    }
}

void query() {
    if (capacity) {
        printf("%d\n", top->val);
    } else {
        puts("Empty");
    }
}

void size() {
    printf("%d\n", capacity);
}

int main() {
    int n;
    scanf("%d", &n);
    while (n--) {
        char szCmd[6];
        int value;
        scanf("%s", szCmd);
        if (szCmd[0] == 'p') {
            if (szCmd[1] == 'u') {
                scanf("%d", &value);
                push(value);
            } else if (szCmd[1] == 'o') {
                pop();
            }
        } else if (szCmd[0] == 'q') {
            query();
        } else if (szCmd[0] == 's') {
            size();
        }
    }
    return 0;
}