int led = 5;
int bright = 0 ; 
int incr = 5;
int time = 50;
void setup() {
  // put your setup code here, to run once:
  pinMode(led, OUTPUT);
}

void loop() {
  // brightness low to high, hight to low
  //analogWrite function, pin no. 5 pr voaltage control krne lgega
  analogWrite(led , bright); //pwm value write
  delay(time);
  bright+=incr;
  if(bright<=0 || bright>=255)//because aurduino is 8 bit microcontroller
  {
    incr = -incr;
  }

}