const int led[4] = {13,12,27,26};
const int button[4] = {2,4,18,19};
boolean buttonState = HIGH;

void setup() {
  for (int i=0;i<4;i++){
  pinMode (led[i],OUTPUT);
  pinMode (button[i],INPUT_PULLUP);
  }
}

void loop() {
  for (int i=0;i<4;i++){
  if (digitalRead (button[i])==LOW){
    delay(50);
    if (buttonState==HIGH){
      digitalWrite(led[i],!digitalRead(led[i]));
      delay(200);
    }
  buttonState==LOW;
  } else {
      buttonState==HIGH;
    }
  }
}