const int pb1 = 8;// Push Button1
const int pb2 = 9;// Push Button2
const int led1 = 4;
const int led2 = 5;
const int led3 = 6;
const int led4 = 7;

int j;

void setup(){
  pinMode(pb1, INPUT);
  pinMode(pb2, INPUT);
  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
  pinMode(led4, OUTPUT);

Serial.begin(9600);
}

void loop(){
  int nilaiPb1 = digitalRead(pb1);
  int nilaiPb2 = digitalRead(pb2);
 
  if(nilaiPb1==HIGH) {
  j++;
  if (j<4) j=4;
  }
 
  if(nilaiPb2==HIGH) {
  j--;
  if (j<1) j=1;
  }

  switch (j) {
    case 1:
    digitalWrite(led1, HIGH);
    digitalWrite(led2, LOW);
    digitalWrite(led3, LOW);
    digitalWrite(led4, LOW);
    break;
     case 2:
    digitalWrite(led1, LOW);
    digitalWrite(led2, HIGH);
    digitalWrite(led3, LOW);
    digitalWrite(led4, LOW);
    break;
     case 3:
    digitalWrite(led1, LOW);
    digitalWrite(led2, LOW);
    digitalWrite(led3, HIGH);
    digitalWrite(led4, LOW);
    break;
     case 4:
    digitalWrite(led1, LOW);
    digitalWrite(led2, LOW);
    digitalWrite(led3, LOW);
    digitalWrite(led4, HIGH);
    break;
    default:
    digitalWrite(led1, LOW);
    digitalWrite(led2, LOW);
    digitalWrite(led3, LOW);
    digitalWrite(led4, LOW);
    break;
  }

Serial.println();
}