I always do just from practice
TolpuddleSartre:
Isn't one of the USPs of Arduino that you don't need to write prototypes for forward references?
Good point.
I took OP at his word, but I don't get any error when compiling the first version of his sketch.
I always prototype out of habit.
Also, he is using 1.6.9 of the IDE. Not sure if that makes a difference.
I am using 1.8.3 on Linux