What is the purpose of a declaration like int (x); or int (x) = 10;

Question

If you look at the grammar for *declarator*s in §8/4 you\'ll notice that a noptr-declarator can be written as (ptr-declarator

Answer 1

You're asking the wrong question. The correct question is:

What is the purpose of disallowing such a declaration?

The answer is: there is none.

So, given that this syntax is allowed as a side-effect of rules elsewhere, this is what you get.