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Numio

Online C Compiler — Numio

Compile and run C code online with Clang in your browser. C17, scanf input and compile errors with line numbers. Free, no sign-up, nothing uploaded.

Runs in your browser · No sign-up

Code (C)

Ctrl/⌘ + Enter to run

input() and io.read() read these lines in order.

Output

Code runs locally in your browser; it is not uploaded.

How to use

  1. Write or paste C code with a main function.
  2. Optional: type input for scanf or getchar in the input box.
  3. Press Run (or Ctrl/⌘ + Enter) to compile and run.

Example

// C example
#include <stdio.h>

int main(void) {
    const char *names[] = {"Ada", "Alan"};
    for (int i = 0; i < 2; i++) {
        printf("Hello, %s!\n", names[i]);
    }

    int sum = 0;
    for (int i = 1; i <= 100; i++) {
        sum += i;
    }
    printf("Sum of 1 to 100: %d\n", sum);
    return 0;
}

Details and limitations

Code is compiled to a WebAssembly (WASI) program by Clang, itself running as WebAssembly. The toolchain (about 25 MB) downloads on first use and is cached afterwards.

Compiling takes a few seconds and does not count toward the 10-second run limit. Compile errors are shown with line numbers.

FAQ

Which C standard and compiler are used?

C17, compiled by the real Clang compiler running in your browser as WebAssembly.

How is it different from compiling on my computer?

The program is 32-bit, so int, long and pointers are 4 bytes. Threads and networking are not available, and files exist only in memory.

Is my code uploaded to a server?

No. Your code is compiled and run entirely in your browser. Only the compiler is downloaded from a public CDN (jsDelivr) on first use.

Format references

Tool page updated: