#define SW1 4
#define SW2 3
#define SW3 2
#define BUZZER  10
#define NOTE_C  523
#define NOTE_D  587
#define NOTE_E  659

void setup() {
  // put your setup code here, to run once:
  pinMode(SW1, INPUT_PULLUP);
  pinMode(SW2, INPUT_PULLUP);
  pinMode(SW3, INPUT_PULLUP);
  pinMode(BUZZER, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  if(digitalRead(SW1)==LOW){
    tone(BUZZER,NOTE_C);
  }else if(digitalRead(SW2)==LOW){
    tone(BUZZER,NOTE_D);
  }else if(digitalRead(SW3)==LOW){
    tone(BUZZER,NOTE_E);
  }else{
    noTone(BUZZER);
  }
}