Macro with two names

Projects Programming
10 
#define MY_PIN 6

Then if your sketch says:

digitalRead(MY_PIN);

the pre-processor will do:

digitalRead(6);

before the compiler does it's job.

Now if you have

#define MY_PIN 6
#define LIMIT 6

Then if your sketch says:

for (int i = 0 ; i < LIMIT ; i++) digitalRead(MY_PIN);

the pre-porcessor will do: :

for (int i = 0 ; i < 6 ; i++) digitalRead(6);

before the compiler does it's job.