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#define LED_PIN 6
#define NUM_OF_VALUES 3

String incomingString ="";
int incomingValues[3NUM_OF_VALUES];

void setup()
{
  Serial.begin(9600);
  pinMode(LED_PIN, OUTPUT);
}

void loop()
{
  if (Serial.available() > 0)
  {
    incomingString = Serial.readStringUntil('\n');
    split(incomingString, incomingValues, NUM_OF_VALUES);
  }
  
  analogWrite(LED_PIN, incomingValues[0]);
}

void split(String inputString, int *returnData[], int numOfValues)
{
  int index = 0;
  int lastPos = 0;
  
  for(int i=0; i<inputString.length();i++)
  {
    if(inputString.charAt(i) == ',' && index < numOfValues)
    {
      String tempStr = inputString.substring(lastPos,i-1);
      returnData[index] = tempStr.toInt();
      index++;
      lastPos = i+1;
    }
  }
}