/* 
The main algorithm of the following program was written by irenx's site and I made changes to it.
irenx's website address: https://irenx.ir/arduino/calculator-arduino-keypad/ 
Many thanks for the good site irenx.
*/

#include <LiquidCrystal.h> //Header file for LCD from https://www.arduino.cc/en/Reference/LiquidCrystal
#include <Keypad.h> //Header file for Keypad from https://github.com/Chris--A/Keypad

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] = { 0, 1, 2, 3 };// Connect keypad ROW0, ROW1, ROW2 and ROW3 to these Arduino pins.
byte colPins[COLS] = { 4, 5, 6, 7 }; // Connect keypad COL0, COL1 and COL2 to these Arduino pins.

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

const int rs = 8, en = 9, d4 = 10, d5 = 11, d6 = 12, d7 = 13; //Pins to which LCD is connected
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

 long Num1,Num2,Number;
 char key,action;
 boolean result = false;
 
void setup() {
  Serial.begin(9600);
  lcd.begin(16, 2); //We are using a 16*2 LCD display
  lcd.setCursor(3,0);
  lcd.print("Calculator");
  lcd.setCursor(3,1);
  lcd.print("negin_b2001"); //Display a intro message
  delay(2000); //Wait for display to show info
  lcd.clear(); //Then clean it
}

void loop() {
  
key = kpd.getKey(); //storing pressed key value in a char

if (key!=NO_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;action=' ';}

//.........Key 1.........
  if (key == '1'){ //If Button 1 is pressed
    Serial.println ("Button 1"); 
    if (Number==0){
      Number=1;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 1; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}

//.........Key 4.........
  if (key == '4'){ //If Button 4 is pressed
    Serial.println ("Button 4"); 
    if (Number==0){
      Number=4;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 4; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}

//.........Key 7.........    
  if (key == '7'){ //If Button 7 is pressed
    Serial.println ("Button 7");
    if (Number==0){
      Number=7;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else {
      Number = (Number*10) + 7; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}

//.........Key 0......... 
  if (key == '0'){
    Serial.println ("Button 0"); //Button 0 is Pressed
    if (Number==0){
      Number=0;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 0; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}

//.........Key 2.........    
  if (key == '2'){ //Button 2 is Pressed
    Serial.println ("Button 2"); 
    if (Number==0){
      Number=2;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 2; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}

//.........Key 5.........
  if (key == '5'){
    Serial.println ("Button 5"); 
    if (Number==0){
      Number=5;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 5; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}

//.........Key 8.........    
  if (key == '8'){
    Serial.println ("Button 8"); 
    if (Number==0){
      Number=8;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 8; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}} 

//.........Key #.........  
  if (key == '#'){
    Serial.println ("Button Equal"); 
    Num2=Number;
    result = true;}

//.........Key 3.........    
  if (key == '3'){
    Serial.println ("Button 3"); 
    if (Number==0){
      Number=3;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 3; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}

//.........Key 6.........    
  if (key == '6'){
    Serial.println ("Button 6"); 
    if (Number==0){
      Number=6;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 6; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}

//.........Key 9.........    
  if (key == '9'){
    Serial.println ("Button 9");
    if (Number==0){
      Number=9;
      if(Num1==0){
        lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}
    else{
      Number = (Number*10) + 9; //Pressed twice
      if(Num1==0){
        lcd.print("");lcd.print(action);lcd.print(Number);}
      else{
        lcd.print(Num1);lcd.print(action);lcd.print(Number);}}}  

//.........Key A || B || C || D.........    
  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 = '+';
    lcd.print(Num1);lcd.print(action);}
     if (key == 'B')
    {Serial.println ("Subtraction"); action = '-'; 
    lcd.print(Num1);lcd.print(action);}
     if (key == 'C')
    {Serial.println ("Multiplication"); action = '*';
    lcd.print(Num1);lcd.print(action);}
     if (key == 'D')
    {Serial.println ("Devesion"); action = '/';
    lcd.print(Num1);lcd.print(action);}  

    delay(100);
  } 
}

void CalculateResult()
{
  if (action=='+'){
    Number = Num1+Num2;
    lcd.print(Num1);lcd.print(action);lcd.print(Num2);lcd.print("=");lcd.print(Number);
    result=false;}

  if (action=='-'){
    Number = Num1-Num2;
    lcd.print(Num1);lcd.print(action);lcd.print(Num2);lcd.print("=");lcd.print(Number);
    result=false;}

  if (action=='*'){
    Number = Num1*Num2;
    lcd.print(Num1);lcd.print(action);lcd.print(Num2);lcd.print("=");lcd.print(Number);
    result=false;}

  if (action=='/'){
    Number = Num1/Num2;
    lcd.print(Num1);lcd.print(action);lcd.print(Num2);lcd.print("=");lcd.print(Number);
    result=false;} 
}