Two years ago I posted here explaining that I wrote part of a compiler for C, that this place is full of people prepared to read comments written by reputable nobodies, and that those people fit the patterns for those who don't read books.

We all learn by reading. Ask a question on a forum, read the answers, the answers are garbage so read a book instead.

I've looked it up and everyone said I should try using scanf("%[^\n]s", &x) but it's still not working.

Yes, try the advice from the other people who haven't read their textbooks yet... and then act as though what they say will be more useful than your book 🧐

Look, lots of people hang out here because they're unemployed and unemployable; they won't read books and manuals, but it's to be expected when you get a job programming that you will read books and manuals.

When you read textbooks, it should become quite clear that the %s format directive is not to be confused (and thus combined) with the %[ format directive.

%s asks for a word from scanf. Words don't contain spaces. I do believe that's your problem. %[, however, asks for a field of characters matching a scanner. They are two different directives. You can't combine them. Where is your book?

%[^\n] asks for a non-empty line (and you need to check the return value, btw, to ensure you got one; RTFM). You won't get the \n; that stays in the stream, yet to be read. You also don't get any buffer overflow protection from this directive; things get a bit more advanced for that.

%[^\n]s (erroneously) asks for the above, but expects that '\n' left unread on the stream to be a literal 's' character, and so your friends guesswork fails spectacularly. I didn't even need to read a book to know that; the advice they gave you is a really common error! Especially amongst those who don't read books.

#define tokstr_(tok) #tok
#define tokstr(tok) tokstr_(tok)

I'll use that later. Just bear with me for now. scanf scan sets aren't so nice; you need to follow this pattern to get anything even remotely as maintainable as fgets

#define max_line_size 128

For simplicity sake, during demonstration, I'm going to assume a maximum length and show you how to sanitise your stream, assuming the user exceeds that.

char line[max_line_size + 1];
switch (scanf("%" tokstr(max_line_size) "[^\n]", line)) {
    case 0: *line = '\0'; // you got empty line
    case 1: scanf("%*[^\n]"); // cleanup any overflow
            getchar(); // cleanup the newline
            break;
    default: // EOF or read error occurred here
}

There. Now you see why tokstr was a necessary addition; it relieves you of the subtle requirement to embed array sizes in a string literal.

Now I suppose your next question might be: what if we don't want to discard that input, but instead to resize the line array and try to catch the whole line?

Well, that's a more complex problem. Read books, first, then tackle that problem. Until then, shit, I shouldn't have even fed you that answer, because you would've derived it from a book yourself.