Distance switch

#define trig 2
#define echo 4
#define relay 8

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

void loop() {
 digitalWrite(trig, LOW);
 delayMicroseconds(2);
 digitalWrite(trig, HIGH); 
 delayMicroseconds(10);
 digitalWrite(trig, LOW);

long t = pulseIn (echo,HIGH);

long inches = t/74/2;
long cm = t/29/2;

Serial.print(inches);
Serial.print("in\t");
Serial.print(cm);
Serial.println("cm");


if (cm>30){
  digitalWrite(relay,HIGH);
 
  
}
else {
digitalWrite(relay, LOW);
}

}