Code 4

void setup() {
  // put your setup code here, to run once:
  pinMode(13, OUTPUT); // --> 9
  pinMode(12, OUTPUT); // --> 8
  pinMode(14, OUTPUT); // --> 7
  pinMode(27, OUTPUT); // --> 6
  pinMode(26, OUTPUT); // --> 5    ---> +7 = Einerstelle
  pinMode(25, OUTPUT); // --> 4
  pinMode(33, OUTPUT); // --> 3
  pinMode(15, OUTPUT); // --> 15
  pinMode(2, OUTPUT); // --> 12
  pinMode(4, INPUT); // --> Potentiometer
  pinMode(32, INPUT); // R1 = 10kOhm
  Serial.begin(9600);
}

void loop() {
    double read_ = (analogRead(32)*3.3/4096.); // =U1
    double erg = read_/10000; //I1 = I2
    erg = (3.3-read_)/erg; //= R2
    double enderg = (((erg/10000)-1)/(-0.043))+25;
    int z = (int)enderg % 10;
    int e = (int)enderg / 10;
      reset();
      digitalWrite(2, LOW);
      digitalWrite(15, HIGH);
      justDoIt(e);
      delay(5);
      reset();
      digitalWrite(15, LOW);
      digitalWrite(2, HIGH);
      justDoIt(z);
      delay(5);
}

void reset(){
  digitalWrite(13, HIGH);
  digitalWrite(12, HIGH);
  digitalWrite(14, HIGH);
  digitalWrite(27, HIGH);
  digitalWrite(26, HIGH);
  digitalWrite(25, HIGH);
  digitalWrite(33, HIGH);
}

void zero(){
  digitalWrite(33, LOW);//3
  digitalWrite(25, LOW);//4
  digitalWrite(26, LOW);//5
  digitalWrite(27, LOW);//6
  digitalWrite(14, LOW);//7
  digitalWrite(12, LOW);//8
}

void one(){
  digitalWrite(25, LOW);//4
  digitalWrite(26, LOW);//5
}

void two(){
  digitalWrite(33, LOW);//3
  digitalWrite(25, LOW);//4
  digitalWrite(13, LOW);//9
  digitalWrite(27, LOW);//6
  digitalWrite(14, LOW);//7
}

void three(){
  digitalWrite(33, LOW);//3
  digitalWrite(25, LOW);//4
  digitalWrite(26, LOW);//5
  digitalWrite(27, LOW);//6
  digitalWrite(13, LOW);//9
}

void four(){
  digitalWrite(25, LOW);//4
  digitalWrite(26, LOW);//5
  digitalWrite(12, LOW);//8
  digitalWrite(13, LOW);//9
}

void five(){
  digitalWrite(33, LOW);//3
  digitalWrite(12, LOW);//8
  digitalWrite(13, LOW);//9
  digitalWrite(26, LOW);//5
  digitalWrite(27, LOW);//6
}

void six(){
  digitalWrite(33, LOW);//3
  digitalWrite(26, LOW);//5
  digitalWrite(27, LOW);//6
  digitalWrite(14, LOW);//7
  digitalWrite(12, LOW);//8
  digitalWrite(13, LOW);//9
}

void seven(){
  digitalWrite(33, LOW);//3
  digitalWrite(25, LOW);//4
  digitalWrite(26, LOW);//5
}

void eight(){
  digitalWrite(33, LOW);//3
  digitalWrite(25, LOW);//4
  digitalWrite(26, LOW);//5
  digitalWrite(27, LOW);//6
  digitalWrite(14, LOW);//7
  digitalWrite(12, LOW);//8
  digitalWrite(13, LOW);//9
}

void nine(){
  digitalWrite(33, LOW);//3
  digitalWrite(25, LOW);//4
  digitalWrite(26, LOW);//5
  digitalWrite(27, LOW);//6
  digitalWrite(12, LOW);//8
  digitalWrite(13, LOW);//9
}

void justDoIt(int n){
  switch (n) {
    case 0:
    zero();
    break;
    case 1:
    one();
    break;
    case 2:
    two();
    break;
    case 3:
    three();
    break;
    case 4:
    four();
    break;
    case 5:
    five();
    break;
    case 6:
    six();
    break;
    case 7:
    seven();
    break;
    case 8:
    eight();
    break;
    case 9:
    nine();
    break;
  }
}