Struggling with compiler flags

Very basic question, I know. Nevertheless, still having troubles to resolve it...
Consider the following code in render.cpp

#ifdef	MYFLAG
    	(void)printf("MYFLAG is defined\n");
#else
    	(void)printf("MYFLAG is NOT defined\n");
#endif

In "Make Parameters:" I added MYFLAG=1 but still, MYFLAG is not known in render.cpp.
How to define compiler flags properly?

Those are flags passed to make, not values that are defined. So you need to pass CPPFLAGS=-DMYFLAG=1

It works perfectly. Thanks!