int led1=10;
 int led2=11;
 int led3=12;
 int led4=13;
 int incr=7;
 int decr=8;
 int ledcounter=0;

void setup() 
{
pinMode(led1, OUTPUT);
pinMode(led2, OUTPUT);
pinMode(led3, OUTPUT);
pinMode(led4, OUTPUT);
pinMode(incr, INPUT);
pinMode(decr,INPUT);  
}

void loop() {
  if(digitalRead(incr))
  {
    ledcounter++;
  }
  if(digitalRead(decr));
  {
    ledcounter--;
  }
  switch(ledcounter)
  {
    case 0:
    digitalWrite(led1, LOW);
    digitalWrite(led2, LOW);
    digitalWrite(led3, LOW);
    digitalWrite(led4, LOW);
    break;
    case 1:
    digitalWrite(led1, HIGH);
    digitalWrite(led2, LOW);
    digitalWrite(led3, LOW);
    digitalWrite(led4, LOW);
    break;
    case 2:
    digitalWrite(led1, HIGH);
    digitalWrite(led2, HIGH);
    digitalWrite(led3, LOW);
    digitalWrite(led4, LOW);
    break;
    case 3:
    digitalWrite(led1, HIGH);
    digitalWrite(led2, HIGH);
    digitalWrite(led3, HIGH);
    digitalWrite(led4, LOW);
    break;
    case 4:
    digitalWrite(led1, HIGH);
    digitalWrite(led2, HIGH);
    digitalWrite(led3, HIGH);
    digitalWrite(led4, HIGH);
    break;
  } 

  delay(100);
}