int ledPin[] = {4,5,6,7};
void setup()
{
 for (int i =0;i<4;i++)
 {
 pinMode(ledPin[i], OUTPUT);
 }
}
void loop()
{
 for (byte counter =0;counter<=15; counter++)
 {
 displayBinary(counter);
 delay(500);
 }
}
void displayBinary(byte numToShow)
{
 for (int i =0;i<4;i++)
 {
 if (bitRead(numToShow, i)==1)
 {
 digitalWrite(ledPin[i], HIGH);
 }
 else
 {
 digitalWrite(ledPin[i], LOW);
 }
 }
}