int sen = A0;
int led = 9;

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

void loop() {
  int a = analogRead(sen);
  a = constrain(a, 100, 1023);
  int b = map(a, 100, 1023, 0, 255);
  int c = map(a, 100, 1023, 0, 100);
  analogWrite(led, b);
  Serial.println(c);
  delay(100);
}