#include <LiquidCrystal.h>
#include <Keypad.h>

LiquidCrystal lcd(13, 12, 11, 10, 1, 0);

const byte ROWS = 4; // Four rows
const byte COLS = 4; // Four columns
// Define the Keymap
char keys[ROWS][COLS] = 
{
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};

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

Keypad kpd = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );
 long Num1,Num2,Number;
 char key,symbol;
 boolean result = false;
 
void setup() 
{  
  lcd.print("Arduino Calculator");
  lcd.setCursor(0, 1);   // set the cursor to column 0, line 1
  delay(5000); // Wait for display to show info
  lcd.clear();
}
void loop() 
{
key = kpd.getKey(); //storing pressed key value in a char format
if (key!=NO_KEY)
button();
if (result==true)
Calculations();
DisplayResult();   
}
void button()
{ 
    lcd.clear();
    if (key=='*') //If cancel is pressed
    {
     lcd.print("CLEAR"); Number=Num1=Num2=0; result=false;
     Serial.println("CLEAR");
    }
     if (key == '1') //If 1 is pressed
    {
    lcd.print("1"); 
    Serial.println("1");
    if (Number==0)
    Number=1;
    else
    Number = (Number*10) + 1; //Pressed twice
    }
     if (key == '4') //If 4 is pressed
    {
    lcd.print("4");
    Serial.println("4"); 
    if (Number==0)
    Number=4;
    else
    Number = (Number*10) + 4; //Pressed twice
    }
    
     if (key == '7') //If 7 is pressed
    {lcd.print("7");
    Serial.println("7");
    if (Number==0)
    Number=7;
    else
    Number = (Number*10) + 7; //Pressed twice
    }
  
    if (key == '0')
    {lcd.print("0"); //0 is Pressed
    Serial.println("0");
    if (Number==0)
    Number=0;
    else
    Number = (Number*10) + 0; //Pressed twice
    }
    
     if (key == '2') //2 is Pressed
    {lcd.print("2"); 
    Serial.println("2");
     if (Number==0)
    Number=2;
    else
    Number = (Number*10) + 2; //Pressed twice
    }
     if (key == '5')
    {lcd.print("5"); 
     if (Number==0)
    Number=5;
    else
    Number = (Number*10) + 5; //Pressed twice
    }
    
     if (key == '8')
    {lcd.print("8"); 
    Serial.println("8");
     if (Number==0)
    Number=8;
    else
    Number = (Number*10) + 8; //Pressed twice
    }   
  
    if (key == '#')
    {lcd.print("="); 
    Serial.println("=");
    Num2=Number;
    result = true;
    }
    
     if (key == '3')
    {lcd.print("3"); 
    Serial.println("3");
     if (Number==0)
    Number=3;
    else
    Number = (Number*10) + 3; //Pressed twice
    }
    
     if (key == '6')
    {lcd.print("6"); 
    Serial.println("6");
    if (Number==0)
    Number=6;
    else
    Number = (Number*10) + 6; //Pressed twice
    }
    
     if (key == '9')
    {lcd.print("9");
    Serial.println("9");
    if (Number==0)
    Number=9;
    else
    Number = (Number*10) + 9; //Pressed twice
    }  
      if (key == 'A' || key == 'B' || key == 'C' || key == 'D')
  {
    Num1 = Number;    
    Number =0;
    if (key == 'A')
    {
      lcd.print("+");
      Serial.println("1");
      symbol = '+';
     }
     if (key == 'B')
     {
      lcd.print("-");
      Serial.println("-");
      symbol = '-';
     }
     if (key == 'C')
     {
      lcd.print("*");
      Serial.println("*");
      symbol = '*';
     }
     if (key == 'D')
     {
      lcd.print("/");
      Serial.println("/");
      symbol = '/';
     } 
    delay(100);
  }
}
void Calculations()
{
  if (symbol=='+')
    Number = Num1+Num2;
  if (symbol=='-')
    Number = Num1-Num2;
  if (symbol=='*')
    Number = Num1*Num2;
  if (symbol=='/')
    Number = Num1/Num2; 
}
void DisplayResult()
{
  lcd.setCursor(0, 0);
  lcd.print(Num1); lcd.print(symbol); lcd.print(Num2); 

  if (result==true)
  {
  lcd.print(" ="); lcd.print(Number);//Display the result
  } 
  lcd.setCursor(0, 1);
  lcd.print(Number); //Display the result
}