Ideally the service(?) would let me submit a program written in C, C++, others(?), and present users with a mock terminal interface to run it. Bonus points if there is a way to submit input files or retrieve output files after the program runs.
At which point you may as well just fire up a small VM slap Apache on it (or whatever you prefer) and run your binary as a CGI program behind a page.
Or put another way, hosting a service like this would cost more than hosting a VM, which means an already tiny market just got smaller.
So, while I'm not aware of such a service, I predict it it exists it'll be more expensive than you are prepared to accept.
I get that using a Woordle solver is redundant, so this is an example,not an actual use case, but I'll say it anyway - if you want to share code like this then use JavaScript or set up a server and use PHP or whatever with your C code running on your server.
I am not proposing to try and make such a thing myself, but I'm hoping someone has done it. It would be widely useful. Programming languages are a dime a dozen but sharing simple programs written with them is problematic when there is such a disconnect between the I/O model of most programming languages plus their standard libraries and the realities of web architecture and plumbing. But adapting one to another is something people do. Web REPLs are a thing, I just want a web REPL taken to the next level.
Surely it should be possible to do "Hello World" on the web.
Maybe Replit too?