int trig = A1;
int echo = A0;
int led = A2;
int led2 = A3;
int led3 = A4;


void setup() {
  pinMode(trig, OUTPUT);
  pinMode(echo, INPUT);
  pinMode(led, OUTPUT);
  pinMode(led3, OUTPUT);
  pinMode(led2, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  digitalWrite(trig, LOW);
  delayMicroseconds(2);

  digitalWrite(trig, HIGH);
  delayMicroseconds(10);

  digitalWrite(trig, LOW);
 long duration = pulseIn(echo, HIGH);
  // Calculating the distance

  int dist = duration * 0.034/2;
  // if you will change the value of sound speed in air which is (0.034) correct
  if(dist <= 25){
    Serial.println("CM");
    Serial.print(dist);
    digitalWrite(led, HIGH);
    digitalWrite(led2, LOW);
    digitalWrite(led3, LOW);

  }

  else if(dist <= 50){
    Serial.println(dist);
    Serial.print("CM");
    digitalWrite(led2, HIGH);
    digitalWrite(led, LOW);
    digitalWrite(led3, LOW);

  }
  else if(dist <= 100){
    Serial.println(dist);
    Serial.print("CM");
    digitalWrite(led3, HIGH);
    digitalWrite(led, LOW);
    digitalWrite(led2, LOW);

  }
  else{
    digitalWrite(led, LOW);
    digitalWrite(led3, LOW);
    Serial.println(dist);
    Serial.println("CM");
    digitalWrite(led2, LOW);
  }
}