#include <LiquidCrystal_I2C.h> 
#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 4; 


char keys[ROWS][COLS] = {

  {'1','2','3','A'},

  {'4','5','6','B'},

  {'7','8','9','C'},

  {'*','0','#','D'}

};

byte colPins[COLS] = {5,4,3,2}; 
byte rowPins[ROWS] = {9,8,7,6};

Keypad kpd = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS ); 

LiquidCrystal_I2C lcd(0x27, 16, 2);

 long Num1,Num2,Number;
 char key,action;
 boolean result = false;
 
void setup() {
  Serial.begin(9600);
  lcd.init(); 
  lcd.print("Kalkulator Siap!"); 
  lcd.setCursor(0, 1);   
  lcd.print("A=+ B=- C=* D=/"); 

   delay(6000); 
    lcd.clear(); 
}

void loop() {
  
key = kpd.getKey();

if (key!=NO_KEY)
DetectButtons();

if (result==true)
CalculateResult();

DisplayResult();   
}

void DetectButtons()
{ 
     lcd.clear(); 
    if (key=='*') 
    {Serial.println ("Button Cancel"); Number=Num1=Num2=0; result=false;}
    
     if (key == '1') 
    {Serial.println ("Button 1"); 
    if (Number==0)
    Number=1;
    else
    Number = (Number*10) + 1; 
    }
    
     if (key == '4') 
    {Serial.println ("Button 4"); 
    if (Number==0)
    Number=4;
    else
    Number = (Number*10) + 4; 
    }
    
     if (key == '7') 
    {Serial.println ("Button 7");
    if (Number==0)
    Number=7;
    else
    Number = (Number*10) + 7; 
    } 
  

    if (key == '0')
    {Serial.println ("Button 0"); 
    if (Number==0)
    Number=0;
    else
    Number = (Number*10) + 0; 
    }
    
     if (key == '2') 
    {Serial.println ("Button 2"); 
     if (Number==0)
    Number=2;
    else
    Number = (Number*10) + 2; 
    }
    
     if (key == '5')
    {Serial.println ("Button 5"); 
     if (Number==0)
    Number=5;
    else
    Number = (Number*10) + 5; 
    }
    
     if (key == '8')
    {Serial.println ("Button 8"); 
     if (Number==0)
    Number=8;
    else
    Number = (Number*10) + 8; 
    }   
  

    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;
    }
    
     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 ("Division"); action = '/';}  

    delay(100);
  }
  
}

void CalculateResult()
{
  if (action=='+')
    Number = Num1+Num2;

  if (action=='-')
    Number = Num1-Num2;

  if (action=='*')
    Number = Num1*Num2;

  if (action=='/')
    Number = Num1/Num2; 
}

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(" ="); lcd.print(Number);} //Display the result
  
  lcd.setCursor(0, 1);   // set the cursor to column 0, line 1
  lcd.print(Number); //Display the result
}