>Run this example:
>

>#define INP
>#define REF
>#define OUT
>
>? INP REF OUT && Variable 'REF' is not found.
>? INP REF     && Variable 'REF' is not found.
>? INP
>
>? INP OUT REF && Variable 'OUT' is not found.
>? INP OUT     && Variable 'OUT' is not found.
>

>
>
>Why preprocesor ignoring each second constant at compiling?

Better question: why didn't it catch that your #define statements are bad? The expressions are missing. Yet it compiles without a hitch.

I tried inserting a wait statement between the #define lines, just to see whether it catches anything from the next line, but it doesn't, the result is still the same.