Run C++ 20 online

What's in C++ 20

• Concepts — first-class constraints on templates. No more SFINAE stacks.
• Ranges — pipeable operations over containers.
• Coroutines — `co_await`, `co_yield`, `co_return` in the language.

What you get in C++ 20

Clicking "Run now" opens the playground with this exact code and a matching test case — passes on first Run.

#include<iostream>
int main(){int n;std::cin>>n;std::cout<<n*2<<std::endl;return 0;}

How ls-judge runs C++ 20

Every submission is compiled and executed inside its own Firecracker microVM — the same isolation primitive AWS Lambda uses. No shared container, no shared kernel with other users' code. The C++ 20toolchain shipped with the microVM is the real thing (not a browser-side emulation): syscalls behave the way they do in production, and the compile / runtime behaviour matches what you would see on your own machine with that version installed.

Feed stdin from the Tests panel, watch verdicts stream per test case over a WebSocket. Free to use, no sign-up, works from any browser.