#4.4.3.1. 예제 

void setup() {

pinMode(2, INPUT_PULLUP);

pinMode(3, INPUT_PULLUP);

pinMode(4, INPUT_PULLUP);

}

void loop() {

if (!(digitalRead(2) == HIGH)) {

tone(11, 262, 100);

}

if (!(digitalRead(3) == HIGH)) {

tone(11, 294, 100);

}

if (!(digitalRead(4) == HIGH)) {

tone(11, 330, 100);

}

}