Run C 90 online

What's in C 90

• The K&R descendant, made ISO 9899:1990.
• The last version that many teaching curricula start with (deliberately).
• Universal support — every compiler on every platform accepts this.

What you get in C 90

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 90

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 90toolchain 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.