Which many people find unreadable compared to other versions.

And for several reasons.

  * is it (*s)++ or *(s++)?
  * it is not *++s nor ++*s

And I have seen

  *(*s)++

in some places!

It is concise syntax but very confusing.

K&R actually teaches this as a desirable idiom? People should not be recommending K&R to beginners today!

Kernighan spends a page whittling strcpy down to just that, with various intermediate versions. After showing you that version, he describes it like this:

Although this may seem cryptic at first sight, the notational convenience is considerable, and the idiom should be mastered, because you will see it frequently in C programs.