#define IDENTIFIER without a token

Question

What does the following statement mean:

#define FAHAD

I am familiar with the statements like:

#define FAHAD 1

Answer 1

#define FAHAD

this will act like a compiler flag, under which some code can be done. this will instruct the compiler to compile the code present under this compiler option

#ifdef FAHAD
printf();
#else
/* NA */
#endif