C online compiler

What runs your code

Good to know

• Compiles with gcc -O2 and links the maths library, so math.h works without flags.
• C23 is the default standard (__STDC_VERSION__ is 202311), so bool, true and false work without stdbool.h.
• Compiler errors and warnings show with the file name code.c.

Run C from your own code

Send the code and its input to the sync endpoint with an API key, and the output comes back in the response. The API docs cover the async endpoint with callbacks and every response field.

curl -X POST https://api.onlinecompiler.io/api/run-code-sync/ \
  -H "Authorization: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "compiler": "gcc-15",
    "code": "#include <stdio.h>\n\nint main(void) {\n    char name[64];\n    scanf(\"%63s\", name);\n    printf(\"Hello, %s!\\n\", name);\n}",
    "input": "Ada"
  }'

The response has output ("Hello, Ada!\n" here), error, exit_code, time and memory.

Put a runnable C example on your site

The editor above is the embeddable widget. Add the script and a div with your widget key, and your readers can edit and run the code without an account:

<script src="https://onlinecompiler.io/widget.js"></script>

<div class="runcode" data-key="YOUR_WIDGET_KEY" data-lang="gcc-15">
  <script type="text/plain">
    #include <stdio.h>

    int main(void) {
        char name[64];
        scanf("%63s", name);
        printf("Hello, %s!\n", name);
    }
  </script>
</div>

On a platform that takes an iframe but not a script, such as many course sites, use the iframe embed. For Docusaurus, MkDocs, Sphinx and Mintlify, see runnable code examples in docs.

Other languages

Python, C++, Java, C#, F#, Go, Rust, PHP, Ruby, Haskell, TypeScript.

Frequently asked questions

Is this C online compiler free?

Yes. Running C on this page needs no account and shows no ads. To run C from your own app or site, the API and the widget are free up to 100,000 runs a month, commercial use included.

Can my C program read input?

Yes. Type it in the Input tab before you run, and the program reads it from standard input. The whole input is sent when you press Run, so a program can't ask for more while it runs.

Can I use C libraries?

The C standard library and the maths library. There is no package manager, and programs have no network access.

How long can a program run?

Up to 30 seconds, with 512 MB of memory and 2 CPUs. A program still running at 30 seconds is stopped with exit code 124, and output over 64 KB per stream is cut.

Where does my code run?

On our servers, in a fresh gVisor sandbox with no network access that is deleted when the run ends. Each run is kept in execution history with its output; the security page says what is stored.