constexpr uint8_t buttonsPins[5]={2,3,4,5,6};
constexpr uint8_t relayPins[5]={14,15,16,17,18};

void setup() {
  for (uint8_t i=0;i<5;i++) {
    pinMode(buttonsPins[i], INPUT_PULLUP);
    pinMode(relayPins[i], OUTPUT);
    digitalWrite(relayPins[i], HIGH); 
  }
}

void loop() {
  static uint8_t pressButton=0, lastButton = 0;
  for (uint8_t i=0; i<5; i++) 
    if (!digitalRead(buttonsPins[i])) pressButton = i+1;
  if (pressButton != lastButton) { 
    digitalWrite(relayPins[lastButton-1], HIGH);
    digitalWrite(relayPins[pressButton-1], LOW);
    lastButton = pressButton;    
  }
  delay(20);
}