int brightness = 0;
//these two variables are used to store our brightness level during manipulations
int brightnessRev = 255;
int fadeUp = 5;
//the values by which each 'step' of the fade is incremented.
int fadeDown = 5;

int myPins[] = {3, 5, 6, 9, 10, 11};
/*here we are storing our output pins in an array, that allows us to
access the 'next' pin without hard-coding in the program itself
if we wanted to change the pin assignments, we could do it once,
right here, and everything else in the code would stay the same.*/

void setup() {
  //our setup is very simple, we just need to configure each pin as an output
  pinMode(3, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
}

void loop() {
  /*this program basically just increments through each LED, slowly fading it up,
  then moving on to the next and doing the same, until all LEDs are on, then
  starting from the first LED, fades them down. Then the process is repeated in
  reverse, creating a sort of bouncing effect. */

  for(int i=0; i < 6; i++) {
    brightness = 0;
    while(brightness < 255){
      analogWrite(myPins[i], brightness);
      brightness += fadeUp;
      delay(1);
    }
  }
  //basically the goal here is to iterate a 'fade up' routine
  //on each output pin, which is what this for loop does

  for(int i=0; i <6; i++) {
  brightnessRev = 255;
    while(brightnessRev >= 0){
      analogWrite(myPins[i], brightnessRev);
      brightnessRev -= fadeDown;
      delay(1);
    }
  }
  //this for loop does the same thing,
  //but fading the LEDs down.
  delay(125);
  //this delay gives us a slight pause before
  //starting the reverse course
  for(int i=5; i >= 0; i--) {
    brightness = 0;
    while(brightness < 255){
      analogWrite(myPins[i], brightness);
      brightness += fadeUp;
      delay(1);
    }
  }
  for(int i=5; i >= 0; i--) {
  brightnessRev = 255;
    while(brightnessRev >= 0){
      analogWrite(myPins[i], brightnessRev);
      brightnessRev -= fadeDown;
      delay(1);
    }
  }
  delay(125);
}