int led = 10 ;
int i;

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

void loop() {
  
  for(i=0;i<=255;i=i+5)
{
  analogWrite(led, i);
  delay(100);
}
 for(i=0;i<=255;i=i-5)
{
analogWrite(led, i);
  delay(100);
}
  // put your main code here, to run repeatedly:

}