Apart from the new features added in C11 or C17 that others have mentioned, both Beej's Guide and Modern C also cover threads and string encoding (neither of these topics are covered in K&R 2nd edition, as far as I remember). Beej's Guide also has a section on internationalization and one about date/time handling.

But yes, the code is also quite different than in K&R which is relatively terse. See for example this comment in K&R about strcpy on print page 105 (page 119 of the PDF)[1], where after showing two versions of strcpy that are pretty readable and easy to follow, the book says:

> In practice, strcpy would not be written as we showed it above. Experienced C programmers would prefer

    void strcpy(char *s, char *t)
    {
        while ((*s++ = *t++) != '\0')
            ;
    }

Followed by a paragraph saying the condition could be simplified, and that

> the function would likely be written as

    void strcpy(char *s, char *t)
    {
        while (*s++ = *t++)
            ;
    }

Make of that what you will :-)

[1] https://kremlin.cc/k&r.pdf#page=119