int latchPin = 4;//Pin 12 (RCLK) of the shift register to pin 4 on the Arduino – this will be referred to as the “latch pin”
int clockPin = 5;//Pin 11 (SRCLK) of the shift register to pin 5 on the Arduino – this will be referred to as the “clock pin”
int dataPin = 2;//Pin 14 (SER) of the shift register to pin 2 on the Arduino – this will be referred to as the “data pin”
byte leds = 0;//a variable called 'leds' is defined. This will be used to hold the pattern of which LEDs are currently turned on or off. Data of type 'byte' represents numbers using eight bits. Each bit can be either on or off, so this is perfect for keeping track of which of our eight LEDs are on or off.
int currentLED = 0;

void setup()
{
  //The 'setup' function just sets the three pins we are using to be digital outputs.
    pinMode(latchPin, OUTPUT);
    pinMode(dataPin, OUTPUT);
    pinMode(clockPin, OUTPUT);

    leds = 0;
}

void loop()
{
  //In the loop method, we clear the bits in the leds variable at the start of every iteration so that all the bits are set to 0 as we only want to light up one LED at a time. After this we increment or reset the currentLED variable so that we are lighting up the correct LED next.
    leds = 0;

    if (currentLED == 7)
    {
        currentLED = 0;
    }
    else
    {
        currentLED++;
    }

    bitSet(leds, currentLED);

    digitalWrite(latchPin, LOW);
    shiftOut(dataPin, clockPin, LSBFIRST, leds);
    digitalWrite(latchPin, HIGH);

    delay(70);
}