[BOJ] 10828 스택

#include <stack>
#include <cstdio>
#include <cstring>
using namespace std;

int main(){
    int n, x;
    scanf("%d", &n);
    stack<int> stk;
    char op[10];
    for (int i = 0; i < n; i++){
        scanf("%s", op);
        if (strcmp(op, "push") == 0){
            scanf("%d", &x);
            stk.push(x);
        }
        else if (strcmp(op, "pop") == 0){
            if (stk.empty())
                printf("-1\n");
            else{
                printf("%d\n", stk.top());
                stk.pop();
            }
        }
        else if (strcmp(op, "size") == 0)
            printf("%d\n", stk.size());
        else if (strcmp(op, "empty") == 0)
            printf("%d\n", stk.empty());
        else{
            if (stk.empty())
                printf("-1\n");
            else
                printf("%d\n", stk.top());
        }
    }
}