unsigned long changeTime;
int timeDelay = 200;
int ones, tens = 0;
void setup()
{
  for (int i = 0; i <= 13; i++)
    pinMode(i, OUTPUT); //all pins Output
    display_ones(0);
    display_tens(0); 
    delay(300);
}
//array of digits  from 0 to 9
const int number[11] = {0b00000001, 0b11001111, 0b10010010, 0b0000110, 0b11001100, 0b0100100, 0b0100000, 0b0001111, 0b00000000, 0b00000100};

void loop(){
  if ((millis() - changeTime) > timeDelay) {
    ones ++;
    if ( ones > 9){
      ones = 0;
      tens ++;
      if (tens > 9) tens = 0;
    }
    display_ones(ones);
    display_tens(tens);
    changeTime = millis();
  }
}

void display_tens(const int tens){
  int pin1, a; //    
  for (pin1 = 0, a = 0; pin1 < 7; pin1++, a++) {
    digitalWrite(pin1, bitRead(number[tens], a));
  }
}

void display_ones(const int ones){
  int pin2, b;             
  for (pin2 = 7, b = 0; pin2 <= 13; pin2++, b++)  {
    digitalWrite(pin2, bitRead(number[ones], b));
  }
}