unsigned variable over-/under-flow and modulus

[nickgammon]

Hard? Not at all:

void setup ()
{
  Serial.begin(115200);
  byte foo = 0;
  foo = foo - 1;
  Serial.println (foo);
}
void loop () {}

I must do that 10 times a day to confirm this or that works (or not). A useful habit to get into.