Run C 99 online

What's in C 99

• // single-line comments finally standardised.
• Variable-length arrays (VLAs) — later made optional in C11.
• Compound literals, designated initialisers, long long int.

What you get in C 99

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

#include<stdio.h>
int main(){int n;scanf("%d",&n);printf("%d\n",n*2);return 0;}

How ls-judge runs C 99

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 99toolchain 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.