void setup() {
   pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  int vergl = analogRead(A0)*100UL/1024;  // 0 .. 99 ( incl. )
  float messwert = analogRead(A1)/10.0 ; // 0 .. 102.3  ( z. Test )
  digitalWrite(LED_BUILTIN, messwert > vergl);
}