C++: int x[+30] is a valid declaration?

Question

I have been studying arrays these days. I have come across a declaration of an array and initialization of its element in this manner :

int x[+30];
x[+1]=0;

This is confusing me a little. I have the concept in mind that when we write:

x[n]=0;

Then it means:

*(x+n)=0;

Then writing x[+1] would mean *(x++1) and this seems invalid. Please correct me for the mistake I am making in understanding this concept.

Answer 1

x[n] means *((x)+(n)) (note the blackets) and x[+1] means *((x)+(+1)). This is valid.

N3337 5.2.1 Subscripting

The expression E1[E2] is identical (by definition) to *((E1)+(E2))

Answer 2

The + Plus symbol can act as a Unary Operator. It usually has no effect, but the consequence is that it gets removed before the number is resolved. For example:

int x[+30];

Is converted to

int x[operator+(30)];

Which then becomes

int x[30];

Thus, this expression

x[+1] = 0;

Would simply resolve as

x[1] = 0;

It wouldn't resolve as *(x++1), especially since that's not valid syntax in c++.