#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27, 16, 2);  // I2C address 0x27, 16 column and 2 rows

#include <Keypad.h>

const int ROW_NUM = 4;     //four rows
const int COLUMN_NUM = 4;  //four columns

char keys[ROW_NUM][COLUMN_NUM] = {
  { '1', '2', '3', 'A' },
  { '4', '5', '6', 'B' },
  { '7', '8', '9', 'C' },
  { '*', '0', '#', 'D' }
};

byte pin_rows[ROW_NUM] = { 2, 3, 4, 5 };       //connect to the row pinouts of the keypad
byte pin_column[COLUMN_NUM] = { 6, 7, 8, 9 };  //connect to the column pinouts of the keypad

Keypad keypad = Keypad(makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM);

long Num1, Num2, Number;

char action;
char key;
boolean result = false;



void setup() {
  Serial.begin(9600);
  lcd.init();  // initialize the lcd
  lcd.backlight();

  lcd.print("     Digital    ");  //Display a intro message
  lcd.setCursor(0, 1);            // set the cursor to column 0, line 1
  lcd.print("   Calculator   ");  //Display a intro message
  delay(2000);                    //Wait for display to show info
  lcd.clear();                    //Then clean it
}


void loop() {

  key = keypad.getKey();
  if (key) {
    Serial.println(key);
    DetectButtons();
  }

  if (result == true)

    CalculateResult();
  DisplayResult();
}

void DetectButtons() {

  lcd.clear();  //Then clean it

  if (key == '*')  //If cancel Button is pressed
  {
    Serial.println("Button Cancel");
    Number = Num1 = Num2 = 0;
    result = false;
  }

  if (key == '1')  //If Button 1 is pressed

  {
    Serial.println("Button 1");

    if (Number == 0)

      Number = 1;

    else

      Number = (Number * 10) + 1;  //Pressed twice
  }



  if (key == '4')  //If Button 4 is pressed

  {
    Serial.println("Button 4");

    if (Number == 0)

      Number = 4;

    else

      Number = (Number * 10) + 4;  //Pressed twice
  }



  if (key == '7')  //If Button 7 is pressed

  {
    Serial.println("Button 7");

    if (Number == 0)

      Number = 7;

    else

      Number = (Number * 10) + 7;  //Pressed twice
  }




  if (key == '0')

  {
    Serial.println("Button 0");  //Button 0 is Pressed

    if (Number == 0)

      Number = 0;

    else

      Number = (Number * 10) + 0;  //Pressed twice
  }



  if (key == '2')  //Button 2 is Pressed

  {
    Serial.println("Button 2");

    if (Number == 0)

      Number = 2;

    else

      Number = (Number * 10) + 2;  //Pressed twice
  }



  if (key == '5')

  {
    Serial.println("Button 5");

    if (Number == 0)

      Number = 5;

    else

      Number = (Number * 10) + 5;  //Pressed twice
  }



  if (key == '8')

  {
    Serial.println("Button 8");

    if (Number == 0)

      Number = 8;

    else

      Number = (Number * 10) + 8;  //Pressed twice
  }




  if (key == '#')

  {
    Serial.println("Button Equal");

    Num2 = Number;

    result = true;
  }



  if (key == '3')

  {
    Serial.println("Button 3");

    if (Number == 0)

      Number = 3;

    else

      Number = (Number * 10) + 3;  //Pressed twice
  }



  if (key == '6')

  {
    Serial.println("Button 6");

    if (Number == 0)

      Number = 6;

    else

      Number = (Number * 10) + 6;  //Pressed twice
  }



  if (key == '9')

  {
    Serial.println("Button 9");

    if (Number == 0)

      Number = 9;

    else

      Number = (Number * 10) + 9;  //Pressed twice
  }


  if (key == 'A' || key == 'B' || key == 'C' || key == 'D')  //Detecting Buttons on Column 4

  {

    Num1 = Number;

    Number = 0;

    if (key == 'A')

    {
      Serial.println("Addition");
      action = '+';
    }

    if (key == 'B')

    {
      Serial.println("Subtraction");
      action = '-';
    }

    if (key == 'C')

    {
      Serial.println("Multiplication");
      action = '*';
    }

    if (key == 'D')

    {
      Serial.println("Devesion");
      action = '/';
    }


    delay(100);
  }
}


void CalculateResult()

{

  if (action == '+')

    Number = Num1 + Num2;


  if (action == '-')

    Number = Num1 - Num2;


  if (action == '*')

    Number = Num1 * Num2;


   if (action == '/') {
    if (Num2 == 0) {  // Jab Num2 zero hoga
      lcd.clear();           // LCD ko clear karein
      lcd.setCursor(0, 0);   // Cursor ko set karein
      lcd.print("Undefined"); // "Undefined" print karein
      delay(2000);           // 2 second tak dikhayein
      lcd.clear();           // Phir clear kar dein
      result = false;        // Calculation ko cancel karein
      return;                // Function se bahar nikal jayein
    } else {
      Number = Num1 / Num2;  // Agar Num2 zero nahi hai
    }
  }
}
void DisplayResult()

{

  lcd.setCursor(0, 0);  // set the cursor to column 0, line 1

  lcd.print(Num1);
  lcd.print(action);
  lcd.print(Num2);



  if (result == true)

  {
    lcd.print(" =");  //Display the result
    lcd.print(Number);
  }



  lcd.setCursor(0, 1);  // set the cursor to column 0, line 1

  lcd.print(Number);  //Display the result
}