void preprocess(char *string, size_t length) {
    int on_newline = 1;
    for (int i = 0; i < length;) {
        switch (string[i]) {
            case '/': {
                on_newline = 0;
                if (string[i+1] == '*') {
                    for (; i+1 < length; i++) {
                        if (string[i] == '*' && string[i+1] == '/') {
                            string[i] = ' ';
                            string[i+1] = ' ';
                            break;
                        }
                        string[i] = ' ';
                    }
                    continue;
                } else if (string[i+1] == '/') {
                    for (; i < length; i++) {
                        if (string[i] == '\n') {
                            string[i] = ' ';
                            break;
                        }
                        string[i] = ' ';
                    }
                    continue;
                }
                break;
            }
            case '#': {
                if (on_newline) {
                    int escaped = 0;
                    for (i++; i < length; i++) {
                        if (string[i] == '\n' && !escaped) break;
                        escaped = (string[i] == '\\');
                        string[i] = ' ';
                    }
                    break;
                }
            }
            case '\n': on_newline = 1; break;
            default: on_newline = 0; break;
        }
        i++;
    }
}