[Jared Russell]

#define is for CONSTANTS - you want to use a variable such as int or float.

Constants get their value once - you cannot assign them a new one.

Since you seem to be using this data in multiple C files, here is what you need to do:

in tracking.h:

extern int distance_from_wall;

in tracking.c, in the global space (top of file, not inside a function):

int distance_from_wall = 0;

Now your code will work the way you expect.