Using HC-SR04 Sensor to measure distances

1const int trigPin = 10;
2const int echoPin = 9;
3
4float duration,  distance;
5
6void setup() {
7  pinMode(trigPin, OUTPUT);
8  pinMode(echoPin,  INPUT);
9  Serial.begin(9600);
10}
11
12void loop() {
13  digitalWrite(trigPin,  LOW);
14  delayMicroseconds(50);
15  digitalWrite(trigPin, HIGH);
16  delayMicroseconds(50);
17  digitalWrite(trigPin, LOW);
18
19  duration = pulseIn(echoPin, HIGH);
20  distance  = (duration*.0343)/2;
21  Serial.print("Distance: ");
22  if (distance >= 400  || distance <= 2) {
23  Serial.println(" Out of range ");
24}
25else {
26  Serial.print(distance);
27  Serial.println(" cm");
28  delay(500);
29}
30delay(500);
31}