Regarding your question about
#define AA (-64)
See Macro definition and expansion in the C preprocessor:
Object-like macros were conventionally used as part of good programming practice to create symbolic names for constants, e.g.
#define PI 3.14159
... instead of hard-coding those numbers throughout one's code. However, both C and C++ provide the const directive, which provides another way to avoid hard-coding constants throughout the code.
Constants defined as macros have no associated type. Use const where possible.
