int disp_pin[7];	/* array for a-g pins of 7-Segment display */

void define_segment_pins(int a, int b, int c, int d, int e, int f, int g)	/* Assigns 7-segment display pins to board */
{  
  disp_pin[0] = a;
  disp_pin[1] = b;
  disp_pin[2] = c;
  disp_pin[3] = d;
  disp_pin[4] = e;
  disp_pin[5] = f;
  disp_pin[6] = g;
}

void display_number(int num)	/* Function for displaying number (0-9) */
{
  switch(num)
  {
    case 0:
    digitalWrite(disp_pin[0], LOW);	/* Drive disp_pin[0] to LOW */
    digitalWrite(disp_pin[1], LOW);	/* Driving LOW turns on LED segment for common anode display */
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], LOW);
    digitalWrite(disp_pin[4], LOW);
    digitalWrite(disp_pin[5], LOW);
    digitalWrite(disp_pin[6], HIGH); 
    break;
    case 1:
    digitalWrite(disp_pin[0], HIGH);	/* Drive disp_pin[7] to HIGH */
    digitalWrite(disp_pin[1], LOW);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], HIGH);	/* Driving HIGH turns off LED segment for common anode display */
    digitalWrite(disp_pin[4], HIGH);
    digitalWrite(disp_pin[5], HIGH);
    digitalWrite(disp_pin[6], HIGH);
    break;
    case 2:
    digitalWrite(disp_pin[0], LOW);
    digitalWrite(disp_pin[1], LOW);
    digitalWrite(disp_pin[2], HIGH);
    digitalWrite(disp_pin[3], LOW);
    digitalWrite(disp_pin[4], LOW);
    digitalWrite(disp_pin[5], HIGH);
    digitalWrite(disp_pin[6], LOW);
    break;
    case 3:
    digitalWrite(disp_pin[0], LOW);
    digitalWrite(disp_pin[1], LOW);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], LOW);
    digitalWrite(disp_pin[4], HIGH);
    digitalWrite(disp_pin[5], HIGH);
    digitalWrite(disp_pin[6], LOW);
    break;
    case 4:
    digitalWrite(disp_pin[0], HIGH);
    digitalWrite(disp_pin[1], LOW);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], HIGH);
    digitalWrite(disp_pin[4], HIGH);
    digitalWrite(disp_pin[5], LOW);
    digitalWrite(disp_pin[6], LOW);
    break;
    case 5:
    digitalWrite(disp_pin[0], LOW);
    digitalWrite(disp_pin[1], HIGH);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], LOW);
    digitalWrite(disp_pin[4], HIGH);
    digitalWrite(disp_pin[5], LOW);
    digitalWrite(disp_pin[6], LOW);
    break;
    case 6:
    digitalWrite(disp_pin[0], LOW);
    digitalWrite(disp_pin[1], HIGH);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], LOW);
    digitalWrite(disp_pin[4], LOW);
    digitalWrite(disp_pin[5], LOW);
    digitalWrite(disp_pin[6], LOW);
    break;
    case 7:
    digitalWrite(disp_pin[0], LOW);
    digitalWrite(disp_pin[1], LOW);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], HIGH);
    digitalWrite(disp_pin[4], HIGH);
    digitalWrite(disp_pin[5], HIGH);
    digitalWrite(disp_pin[6], HIGH);
    break;
    case 8:
    digitalWrite(disp_pin[0], LOW);
    digitalWrite(disp_pin[1], LOW);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], LOW);
    digitalWrite(disp_pin[4], LOW);
    digitalWrite(disp_pin[5], LOW);
    digitalWrite(disp_pin[6], LOW);
    break;
    case 9:
    digitalWrite(disp_pin[0], LOW);
    digitalWrite(disp_pin[1], LOW);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], LOW);
    digitalWrite(disp_pin[4], HIGH);
    digitalWrite(disp_pin[5], LOW);
    digitalWrite(disp_pin[6], LOW);
    break;
    default:
    digitalWrite(disp_pin[0], HIGH);
    digitalWrite(disp_pin[1], LOW);
    digitalWrite(disp_pin[2], LOW);
    digitalWrite(disp_pin[3], LOW);
    digitalWrite(disp_pin[4], LOW);
    digitalWrite(disp_pin[5], HIGH);
    digitalWrite(disp_pin[6], LOW);
    break;
  }
}

void setup() {
  pinMode(6, OUTPUT);	
  pinMode(7, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  define_segment_pins(28,27,26,22,21,20,19);	/* a-g segment pins to Arduino */
}

void loop() {
  int i;
  for(i = 9; i>=0; i--)
  {
    display_number(i);
    delay(1000);
  }
  for(i = 0; i<=9; i++)
  {
    display_number(i);
    delay(1000);
  }
}