For any C errors that occur during runtime, repl.it just stops running and says "exited with non-zero status". Since a "non-zero status" can be caused by anything from bad printf() formatting to a segfault, it would be really useful if repl.it at least printed the error code (errno), or even strerror(errno).
I tried printing strerror(errno) myself, but it seems repl.it stops running as soon as errno does not equal zero. Nothing was printed after (where I think) the error occured.
Other than that and a few other config-related things, I've greatly appreciated repl.it and found it very useful. Thanks for making it!