byte D1 = 2;
byte D2 = 3;
byte D3 = 4;
byte D4 = 5;

byte A = 6;
byte B = 7;
byte C = 8;
byte D = 9;
byte E = 10;
byte F = 11;
byte G = 12;
byte DP = 13; // decimal point

// Define the input pins for the 7-segment display segments.
const int segmentPins[] = {A, B, C, D, E, F, G, DP};

// Define the input pins for the 7-segment display digits.
const int digitPins[] = {D1, D2, D3, D4};

// For common cathode
uint8_t digitON = LOW;
uint8_t digitOFF = HIGH;

uint8_t segmentON = HIGH;
uint8_t segmentOFF = LOW;

void setup() {
   // Pin initialization.
   for (int i = 0; i < 8; i++) {
      pinMode(segmentPins[i], OUTPUT);
   }
   for (int i = 0; i < 4; i++) {
      pinMode(digitPins[i], OUTPUT);
      digitalWrite(digitPins[i], digitOFF);
   }
}

void loop() 
{
   digitalWrite(D1, digitON); // Turn on the first digit
   digitalWrite(D2, digitON); // Turn on the first digit 
   digitalWrite(D3, digitON); // Turn on the first digit
   digitalWrite(D4, digitON); // Turn on the first digit
   digitalWrite(B, segmentON);
   digitalWrite(C, segmentON);
}