C fixed size array treated as variable size

Question

I have been trying to define a static array with size that should be known at compile time (it\'s a constant expression). It appears that gcc cannot determine the size of th

Answer 1

OP's primary question is well answer here.

To address OP's higher level problem of how to use values like 0.5 or 0.25 in pre-processing, use fractional arithmetic:

#define UNIT_SPEED_LIMIT 12
// #define DISTANCE_MELEE 0.25
// use 25/100 or 1/4 or ...
#define DISTANCE_MELEE_N 1
#define DISTANCE_MELEE_D 4
// #define MOVEMENT_STEPS (unsigned)(2 * UNIT_SPEED_LIMIT / DISTANCE_MELEE)
#define MOVEMENT_STEPS (2u * UNIT_SPEED_LIMIT * DISTANCE_MELEE_D /  DISTANCE_MELEE_N)

struct position (*movements)[MOVEMENT_STEPS + 1];