void output(int d, int c, int b, int a)
{
   if (a == 1) digitalWrite(6, HIGH);
   else if (a == 0) digitalWrite(6, LOW); 
   if (b == 1) digitalWrite(5, HIGH);
   else if (b == 0) digitalWrite(5, LOW);
   if (c == 1) digitalWrite(4, HIGH);
   else if (c == 0) digitalWrite(4, LOW);
   if (d == 1) digitalWrite(3, HIGH);
   else if (d == 0) digitalWrite(3, LOW);
   delay(1000);
}

void setup()
{
}

void loop()
{
   output(0,0,0,0);
   output(0,0,0,1);
   output(0,0,1,0);
   output(0,0,1,1);
   output(0,1,0,0);
   output(0,1,0,1);
   output(0,1,1,0);
   output(0,1,1,1);
   output(1,0,0,0);
   output(1,0,0,1);
}