bool usingInches;
double minimumDistance;

void getInput(bool & inches, double & distance) {
  String answer;

  bool waitingForAnswer = true;
  do {
    Serial.println(F("Which one do you want-- centimeters or inches? \nI only need the first letter of what you choose."));
    while (Serial.available() == 0) ; // wait for something to be read
    answer = Serial.readStringUntil('\n'); // read what's there (or timeout)
    answer.trim(); // get rid of the spaces
    if (toupper(answer[0]) == 'I') {
      Serial.println("You selected inches!");
      inches = true;
      waitingForAnswer = false;
    } else if (toupper(answer[0]) == 'C') {
      Serial.println("You selected centimeters!");
      inches = false;
      waitingForAnswer = false;
    } else {}
  } while (waitingForAnswer);

  Serial.println(F("With that out of the way, please input how far the robot should be from a wall before it freaks out."));

  waitingForAnswer = true;
  char *endPtr = nullptr;
  do {
    Serial.println(F("Input any number here (decimals are welcome!): "));
    while (Serial.available() == 0) ; // wait for something to be read
    answer = Serial.readStringUntil('\n'); // read what's there (or timeout)
    answer.trim(); // get rid of the spaces
    distance = strtod (answer.c_str(), &endPtr);
  } while (endPtr == answer.c_str());
  Serial.print(F("distance = ")); Serial.println(distance, 6);
  Serial.println(F("Ok, You're all set! "));
}

void setup() {
  Serial.begin(115200);
  getInput(usingInches, minimumDistance);
}

void loop() {}