Why does #define INVALID_VALUE -999; give a syntax error when used?

Question

I am trying to compare to a defined constants in C, and I have simplified my program to the following:

#include \"stdio.h\"
#include \"stdlib.h\"
#define INV         


        

Answer 1

Remove the semicolon from your INVALID_VALUE definition.

Macros are replaced lexically (character-by-character) with no understanding of the syntax around them. Your macro INVALID_VALUE is set to -999;, so your if line expands the macro to:

if (test==-999;)

which is invalid C syntax.