int led = 9;
int brightness = 0;
int step = 51;
const int btn = 1;
int btnstate;

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

void loop() {
  if (digitalRead, btn == LOW) {
    ++step;
    if (brightness && brightness < 255){

--step;
}
    }
Serial.println(brightness);
}