void setup() {
  pinMode(2, INPUT_PULLUP);
  pinMode(4, INPUT_PULLUP);
  pinMode(7, INPUT_PULLUP);
  Serial.begin(9600);
}

void loop() {
  boolean b2 = digitalRead(2);
  boolean b4 = digitalRead(4);
  boolean b7 = digitalRead(7);

  Serial.println("Źle podpięte przyciski:" + String(b2 ? " 2," : " ") + String(b4 ? " 4," : "") + String(b7 ? " 7" : ""));
  delay(1000);

}