Arduino 4 Slave

#include <Wire.h>

int pu_button_red = 2;
int pu_led_red = 7;
int pu_relay_red = 10;

int pd_button_white = 4;
int pd_led_white = 8;
int pd_relay_white = 12;


void setup() {
  Serial.begin(9600);
  Wire.begin(0x4);                // join i2c bus with address #4
  Wire.onReceive(receiveEvent); // register event  

  pinMode(pu_button_red, INPUT);
  pinMode(pu_led_red, OUTPUT);
  pinMode(pu_relay_red, OUTPUT);
  
  pinMode(pd_button_white, INPUT);
  pinMode(pd_led_white, OUTPUT);
  pinMode(pd_relay_white, OUTPUT);
}

void loop() {
  
  /* 
    Pull up configuration
  */ 
  
    int pu_button_red_State = digitalRead(pu_button_red);
    if ( pu_button_red_State == LOW) {
      digitalWrite(pu_led_red, HIGH);
      digitalWrite(pu_relay_red, HIGH);
    }
    else {
      digitalWrite(pu_led_red, LOW);
      digitalWrite(pu_relay_red, LOW);
    }

 /* 
    Pull down configuration
  */ 
  
    int pd_button_white_State = digitalRead(pd_button_white);
    if ( pd_button_white_State == HIGH) {
      digitalWrite(pd_led_white, HIGH);
      digitalWrite(pd_relay_white, HIGH);
    }
    else {
      digitalWrite(pd_led_white, LOW);
      digitalWrite(pd_relay_white, LOW);
    }
      


  
}

// function that executes whenever data is received from master
// this function is registered as an event, see setup()
void receiveEvent(int howMany) {
}