// Pins
int button_pins[7] = {13, 12, 11, 10, 9, 8, 7};
int button_pins_length = sizeof(button_pins)/sizeof(button_pins[0]);
int buzzer_pin = 6;

int btn_value = 0;

// Notes
int pitch = 0;
int note_freqs[7] = {523, 587, 659, 698, 783, 880, 987};

void setup() {
  // Set button pins
  for (int i = 0; i < button_pins_length; i++){
    pinMode(button_pins[i], INPUT_PULLUP);
  }

  // Set buzzer pin
  pinMode(buzzer_pin, OUTPUT);
}

void loop() {
  int note = 0;

  // Check each button
  for (int i = 0; i < button_pins_length; i++) {
    btn_value = digitalRead(button_pins[i]);
    if (btn_value == LOW) { // Button pressed
      note = note_freqs[i]; // Set pitch to corresponding note frequency
    } 
  }

  if (note){
    tone(buzzer_pin, note);
  } else {
    noTone(buzzer_pin);
  }
}