int i=0;
void setup() 
{
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);
  pinMode(7, INPUT);
  pinMode(8, INPUT);

}

void loop() 
{
    if(digitalRead(7)==1)
    {
      i++;
    }
    if(digitalRead(8)==1)
    {
    if(i>0)
    {
      i--;
    }
    }
  switch(i)
    {
    case 0:
    digitalWrite(10,LOW);
    digitalWrite(11,LOW);
    digitalWrite(12,LOW);
    digitalWrite(13,LOW);
    break;
    case 1:
    digitalWrite(10,HIGH);
    digitalWrite(11,LOW);
    digitalWrite(12,LOW);
    digitalWrite(13,LOW);
    break;
    case 2:
    digitalWrite(10,HIGH);
    digitalWrite(11,HIGH);
    digitalWrite(12,LOW);
    digitalWrite(13,LOW);
    break;
    
    case 3:
    digitalWrite(10,HIGH);
    digitalWrite(11,HIGH);
    digitalWrite(12,HIGH);
    digitalWrite(13,LOW);
    break;
    
    case 4:
    digitalWrite(10,HIGH);
    digitalWrite(11,HIGH);
    digitalWrite(12,HIGH);
    digitalWrite(13,HIGH);
    break;
    default:
      i=1;
      break;
}
delay(100);
}