Preprocessing in C++

Question

How to make that when I define both instructions at the same time I will get the compilation error? Here I want error

#define ENG
#define POL
#if defined POL
#if defined ENG

Here not

#define ENG
//#define POL
#if defined POL
#if defined ENG

Answer 1

#if defined( ENG ) && defined( POL )
#error You can't define both!
#endif