Cat Detector!

#include <Arduino.h> 
#include <U8g2lib.h> 
#ifdef U8X8_HAVE_HW_SPI 
#include <SPI.h> 
#endif 
#ifdef U8X8_HAVE_HW_I2C 
#include <Wire.h> 
#endif 
U8G2_SSD1306_128X64_NONAME_F_SW_I2C u8g2(U8G2_R0, /* clock=*/ SCL, /* data=*/ SDA, /* reset=*/ U8X8_PIN_NONE);   // All Boards without Reset of the Display 

// Define pins for ultrasonic sensor
int const trigPin = 10;
int const echoPin = 9; 

void setup(void) { 
  u8g2.begin();             // Oled display begins 
  pinMode(trigPin, OUTPUT); // trig pin will have pulses output
  pinMode(echoPin, INPUT);  // echo pin should be input to get pulse width
} 

void loop(void) { 
  int duration, distance; // Duration will be the input pulse width and distance will be the distance to the obstacle in centimeters
  
  // Output pulse with 1ms width on trigPin
  digitalWrite(trigPin, HIGH); 
  delay(1);
  digitalWrite(trigPin, LOW);
  
  duration = pulseIn(echoPin, HIGH); // Measure the pulse input in echo pin
  
  distance = (duration/2) / 29.1;    // Distance is half the duration devided by 29.1 (from datasheet)
     
  // if distance less than 0.5 meter and more than 0 (0 or less means over range) 
    if (distance <= 50 && distance >= 0) {
         u8g2.clearBuffer();                // clear the internal memory 
         u8g2.setFont(u8g2_font_inr30_mf);  // choose a suitable font 
         u8g2.drawStr(0,50,"CAT");          // write something to the internal memory 
         u8g2.sendBuffer();                 // transfer internal memory to the display 
    } else {
         u8g2.clearBuffer();                // clear the internal memory 
         u8g2.sendBuffer();                 // transfer internal memory to the display 
    } 

    delay(30);
}