void setup() 
{
  // initialize serial communication:
  Serial.begin(9600);
  // initializing the LED pins:
  for (int LEDpin = 6; LEDpin <13 ; LEDpin++) {
    pinMode(LEDpin, OUTPUT);
    // here, we have used for loop for initialization
  }
}
void loop() 
{
   int a = 3; // we can specify any variable name
    switch (a) 
    {
      case 1:
        digitalWrite(6, HIGH);
        break;
      case 2:
        digitalWrite(8, HIGH);
        break;
      case 3:
        digitalWrite(11, HIGH);
        break;
      case 4:
        digitalWrite(12, HIGH);
        break;
      default:
        // turn all the LEDs off if all the above cases does not matches:
        for (int LEDpin = 6; LEDpin <13; LEDpin++) 
        {
          digitalWrite(LEDpin, LOW);
        }
    }
  }