题解 | 【模板】栈

#include <iostream>
using namespace std;

int main() {
    int n;
    cin >> n;
    string a;
    int x[n], len=0;
    for (int i=0; i<n; ++i) {
        cin >> a;
        if (a == "pop") {
            if (len > 0) {
                cout << x[--len] << endl;
            }
            else cout << "error" << endl;
        }
        else if (a == "top") {
            if (len > 0) {
                cout << x[len-1] << endl;
            }
            else cout << "error" << endl;
        }
        else {
            int t;
            cin >> t;
            x[len++] = t;
        }
    }
    
}
// 64 位输出请用 printf("%lld")

#include <iostream>
#include <type_traits>
using namespace std;

class stack {
    private:
    int x[100000];
    int top_index = -1;
    public:
    int size() {
        return top_index+1;
    }
    void push(int i) {
        x[++top_index] = i;
    }
    int pop() {
        return x[top_index--];
    }
    int top() {
        return x[top_index];
    }
};

int main() {
    int n;
    cin >> n;
    string a;
    stack x;
    for (int i = 0; i < n; ++i) {
        cin >> a;
        if (a == "pop") {
            if (x.size() > 0) {
                cout << x.pop() << endl;
            } else cout << "error" << endl;
        } else if (a == "top") {
            if (x.size() > 0) {
                cout << x.top() << endl;
            } else cout << "error" << endl;
        } else {
            int t;
            cin >> t;
            x.push(t);
        }
    }

}
// 64 位输出请用 printf("%lld")