#include <Wire.h>//includes the Wire library in Arduino
#include <LiquidCrystal_I2C.h>//includes the LiquidCrystal library in Arduino

LiquidCrystal_I2C lcd(0x27, 20, 4); //Setting the I2C address of the LCD screen and the size of the screen

unsigned long previousMillis = 0;  // to keep track of the previous time value, such as in implementing time-based events or timing operations
const long interval = 1000; // Counting time in milliseconds (1000 ms = 1 second).

unsigned long totalSeconds = 0;// to keep track of the total number of seconds elapsed in a program or a specific task.     
unsigned int seconds = 0;// seconds will have an initial value of 0
unsigned int minutes = 0;// minutes will have an initial value of 0
unsigned int hours = 0;// hours will have an initial value of 0
unsigned int days = 0;// days will have an initial value of 0              

void setup() {
  lcd.init();   // To start using an LCD screen
  lcd.backlight(); // Turn on the backlight of the LCD screen
  lcd.setCursor(0, 0);  //any subsequent text or data written to the LCD will start from this position.
  lcd.print("Time: "); //LCD displays to print text on the LCD    screen. 
}

void loop() {
  unsigned long currentMillis = millis();//will hold the number of milliseconds that have elapsed since the Arduino board started running the current program.

  if (currentMillis - previousMillis >= interval)//allowing to perform actions at specific intervals without pausing the execution of the rest of the code. 
  {
    previousMillis = currentMillis; //updating previousMillis to hold the value of currentMillis

    totalSeconds++;//is an increment operation that increases the value of the variable totalSeconds by 1.
    seconds = totalSeconds % 60;// calculates the remainder when totalSeconds is divided by 60
    minutes = (totalSeconds / 60) % 60;//calculates the remainder when the total number of minutes is divided by 60
    hours = (totalSeconds / 3600) % 24;//calculates the remainder when the total number of hours is divided by 24.
    days = totalSeconds / 86400;//convert a total number of seconds into days

    lcd.setCursor(6, 0);//to set the cursor position on the LCD screen.
    lcd.print(days); //printing the variable days on the LCD screen
    lcd.print("d "); //prints the string "d " on the LCD screen

    lcd.print(hours);//printing the variable hours on the LCD screen
    lcd.print("h ");//prints the string "h " on the LCD screen

    lcd.print(minutes);//printing the variable minutes on the LCD screen
    lcd.print("m ");//prints the string "m " on the LCD screen

    lcd.print(seconds);//printing the variable second at LCD
    lcd.print("s ");//prints the string "s " on the LCD screen
  }
}