A reminder to myself of how to handle array indexing in a "round robin" fashion, using the modulus operator.

array-indexing

//assume variables currentIndex, nextIndex, arrayLength exist

//moving "forward", positive incrementing
nextIndex = (currentIndex + 1) % arrayLength;

//moving "backward", negative incrementing
if(currentIndex == 0){
  nextIndex = arrayLength - 1;
} else {
  nextIndex = (currentIndex - 1) % arrayLength;
}