//1) Predefined Section
#include <LiquidCrystal.h>
#include <Keypad.h>

/*********** LCD ************/
#define rs 12
#define en 13
#define d4 8
#define d5 9
#define d6 10
#define d7 11
LiquidCrystal lcd{rs, en, d4, d5, d6, d7};

/*********** Keypad ************/
#define rows 4
#define cols 4

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

char rowPins[rows] = {0, 1, 2, 3};
char colPins[cols] = {4, 5, 6, 7};

Keypad calcKeypad = Keypad(makeKeymap(keys), rowPins, colPins, rows, cols);

// Variables to store inputs
char key;
int num1 = 0;
int num2 = 0;
char op;
bool num1Entered = false;
bool opEntered = false;

//2) Setup Section
void setup() 
{
  lcd.begin(16, 2);
  lcd.print("A=+,B=-,*=x,D=/");
}

//3) Loop Section
void loop() 
{
  key = calcKeypad.getKey(); 

  if (key)  
  {
    lcd.setCursor(0, 1);
    
    
    if (!num1Entered && isdigit(key)) 
    {
      num1 = key - '0';  // Convert ascii value of key pressed to int
      lcd.print(num1);
      delay(100);
      num1Entered = true;
    }
    
    
    else if (num1Entered && !opEntered && (key == 'A' || key == 'B' || key == '*' || key == 'D'))
    {
      op = key;
      switch (op)
      {
        case 'A': lcd.print("+"); break;
        case 'B': lcd.print("-"); break;
        case '*': lcd.print("*"); break;
        case 'D': lcd.print("/"); break;
      }
      
      delay(100);
      opEntered = true;
    }
    

    else if (num1Entered && opEntered && isdigit(key))
    {
      num2 = key - '0';  // Convert ascii value of key pressed to int
      lcd.print(num2);
      delay(200);
      lcd.setCursor(0,0);
      lcd.print("A=+,B=-,*=x,D=/");
      delay(500);
      lcd.setCursor(0,1);
      

      
      lcd.print("=");
      int result;
      switch (op)
      {
        case 'A': result = num1 + num2; break;
        case 'B': result = num1 - num2; break;
        case '*': result = num1 * num2; break;
        case 'D': result = (num2 != 0) ? num1 / num2 : 0; break;//so no runtime error
        default: result = 0; break;
      }
      lcd.print(result);

      //reset
      num1Entered = false;
      opEntered = false;
      delay(3000); 
      lcd.clear();
      lcd.setCursor(0,0);
      lcd.print("A=+,B=-,*=x,D=/");
    }
  }
}