8.8 Subscripting struct
In C90, arrays that are not lvalues still decay to pointers, and can be subscripted.
However, you must not modify or use them
after the next sequence point, and you must not apply the unary
to them. Arrays of this kind can be subscripted in C90, but they
do not decay to pointers outside C99 mode.
extern struct Subscripting_Struct Subscripting_0(void);
int Subscripting_1 (int index)