Arduino serial data input output

I have created an Arduino sketch that I am using to send and receive data via serial. It works pretty well and doesn't seem go wrong as long as the correct formats are received. Is there anything I could do to improve this/shrink it to clear up some code smells?

String dataString;
void setup() {
 Serial.begin(9600);

 //setup digital pins as inputs pin 3 - 13
 for (int i = 2; i <= 7; i++) {
    pinMode(i, INPUT);
  }
  //setup digital pins as OutPuts  pin 22 - 53
  for (int i = 7; i <= 13; i++) {
    pinMode(i, OUTPUT);
  }



}
void loop() {
  serialDataOutput();
  serialDataInput();
  delay(100);

}


void serialDataOutput() {
  dataString = "";
  for (int i = 0; i <= 13; i++) {
    dataString.concat(i);
    dataString.concat("," + String(digitalRead(i)) + "/");
  }

  for (int i = 14; i <= 18; i++) {
   dataString.concat(i);
   dataString.concat("," + String(analogRead(i - 14)) + "/");
  }
   Serial.println(dataString);
  delay(0);
    }
      void serialDataInput() {
  String Input;
   if (Serial.available() > 0) { // If data is available to read,
    Input = Serial.readStringUntil('\n'); // read it and store it in val
  }
  //  Input = "13,1";
  int commaIndex = Input.indexOf(',');
  //  Search for the next comma just after the first
  int secondCommaIndex = Input.indexOf(',', commaIndex + 1);
  String firstValue = Input.substring(0, commaIndex);
  String secondValue = Input.substring(commaIndex + 1, secondCommaIndex);
  digitalWrite(firstValue.toInt(), secondValue.toInt());
}