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Arduino code help using dtostrf()

I need help with an arduino code that I can't figure out. I am really inexperienced with arduino, so sorry if this seems stupid.

I am trying to get my arduino to measure voltage of 2 analog inputs and send the data to a microSD on a shield.

I know I have to use the dtostrf() function, because a friend told me, and I trust him, but he won't tell me how to do it.

How do I get it to work like this using the dtostrf function?

Thanks

Here is the void loop part of my code, with the incorrect attempt at using the function.

void loop()
{
String dataString = "";
  for (int analogPin = A0; analogPin < A2; analogPin++)
  {
    int sensor = analogRead(analogPin);
    float sensorValue = ((float)(sensor) *(5.0/1023.0));
   dtostrf(sensorValue, A0, A1);
    if (analogPin < A2) {
      dataString += " ";
     
    }
  }

    File dataFile = SD.open("datalog.txt", FILE_WRITE);
   
  if (dataFile) {
    dataFile.println(dataString);
    dataFile.close();
    Serial.println(dataString);
  }

  else {
    Serial.println("error opening datalog.txt");
  }
delay(300000);
}