char n_buttons = 7;
char button_pins[] = {0, 1, 2, 3, 4, 5, 6};
char pin_state[] = {HIGH, HIGH, HIGH, HIGH, HIGH, HIGH, HIGH};

char modKey = (char) MODIFIERKEY_CTRL;

int buttons[7] = {KEY_1, KEY_2, KEY_3, KEY_4, KEY_5, KEY_6, KEY_7};


void setup() {
  // put your setup code here, to run once:
  for (int i = 0; i < n_buttons; ++i) {
    pinMode(button_pins[i], INPUT_PULLUP);
  }
}


void loop() {
  char state = 0;
  for (int i = 0; i < n_buttons; ++i) {
    state = digitalRead(button_pins[i]);
    if (state != pin_state[i]) {
      pin_state[i] = state;
      set_button_state(i, state);
    }
  }
  delay(10);
}


void set_button_state(int button_i, char state) {
  char key = buttons[button_i];

  if (state == LOW) {
    Keyboard.set_modifier(MODIFIERKEY_ALT);
    Keyboard.set_key1(key);
    Keyboard.send_now();
  } else {
    Keyboard.set_modifier(0);
    Keyboard.set_key1(0);
    Keyboard.send_now();
  }
}