Ultra Sonic sensor (SR04)

#include <LiquidCrystal.h>
 
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);
 
int trigPin = 9;
int echoPin = 8;
long distance;
long duration;
 
void setup() {
lcd.begin(16, 2);
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
}
 
void loop() {
  ultra();
  lcd.setCursor(0,0);
  lcd.clear();
  lcd.print("UltraSonic");
 
  lcd.setCursor(0,1);
  lcd.print("distance : ");
  lcd.print(distance);
  lcd.print("cm");
  delay(200);
 
   ultra();
  if (distance <= 10)  {
    digitalWrite(7, HIGH);
    delay(1000);
     digitalWrite(7, LOW);
    delay(1000);   }
  digitalWrite(7, LOW);
}
 
void ultra(){
// Clears the trigPin
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
 
// Sets the trigPin on HIGH state for 10 micro seconds
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
 
// Reads the echoPin, returns the sound wave travel time in microseconds
duration = pulseIn(echoPin, HIGH);
 
// Calculating the distance
distance= duration*0.034/2;
}