const int trigpin=9;
  const int echopin=8;
void setup() {
  // put your setup code here, to run once:
  pinMode(trigpin, OUTPUT);
  pinMode(echopin, INPUT);
  pinMode(13, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(11, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
long duration, distance;
digitalWrite(trigpin, LOW);
delayMicroseconds(2);
digitalWrite(trigpin, HIGH);
delayMicroseconds(10);
digitalWrite(trigpin , LOW);

duration=pulseIn(echopin,HIGH);
distance=(duration/2)/29,1;

if (distance>100){
  digitalWrite(11, HIGH);
}else{
  digitalWrite(11, LOW);
}
if (distance>49 && distance<100){
  digitalWrite(12, HIGH);
}else{
  digitalWrite(12, LOW);
}
if (distance<50){
  digitalWrite(13, HIGH);
}else{
  digitalWrite(13, LOW);
}
}