Arduino - While Loop

// These constants won't change:
const int sensorPin = A2;       // pin that the sensor is attached to
const int ledPin = 9;           // pin that the LED is attached to
const int indicatorLedPin = 13; // pin that the built-in LED is attached to
const int buttonPin = 2;        // pin that the button is attached to


// These variables will change:
int sensorMin = 1023;  // minimum sensor value
int sensorMax = 0;     // maximum sensor value
int sensorValue = 0;         // the sensor value


void setup() {
  // set the LED pins as outputs and the switch pin as input:
  pinMode(indicatorLedPin, OUTPUT);
  pinMode (ledPin, OUTPUT);
  pinMode (buttonPin, INPUT);
}

void loop() {
  // while the button is pressed, take calibration readings:
  while (digitalRead(buttonPin) == HIGH) {
    calibrate();
  }
  // signal the end of the calibration period
  digitalWrite(indicatorLedPin, LOW);

  // read the sensor:
  sensorValue = analogRead(sensorPin);

  // apply the calibration to the sensor reading
  sensorValue = map(sensorValue, sensorMin, sensorMax, 0, 255);

  // in case the sensor value is outside the range seen during calibration
  sensorValue = constrain(sensorValue, 0, 255);

  // fade the LED using the calibrated value:
  analogWrite(ledPin, sensorValue);
}

void calibrate() {
  // turn on the indicator LED to indicate that calibration is happening:
  digitalWrite(indicatorLedPin, HIGH);
  // read the sensor:
  sensorValue = analogRead(sensorPin);

  // record the maximum sensor value
  if (sensorValue > sensorMax) {
    sensorMax = sensorValue;
  }

  // record the minimum sensor value
  if (sensorValue < sensorMin) {
    sensorMin = sensorValue;
  }
}