C++ 在线编译器：浏览器里运行 C++ 和 STL

#include <iostream>
using namespace std;

int main() {
    cout << "你好，世界！\n";
    cout << "边玩边学，\n";
    cout << "学会写代码。\n";
    for (int n = 1; n <= 3; n++) {
        cout << "第 " << n;
        cout << " 关已解锁！\n";
    }
}