//libraries for LCD screen
#include <LiquidCrystal.h>
#include <Keypad.h>

//LCD setup -- pins
const int rs=12, en=11, d4=5, d5=4, d6=3, d7=2; 
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);

//Keypad setup
const byte ROWS = 4;
const byte COLS = 4;

char hexaKeys[ROWS][COLS] = {
{'1', '2', '3', '+'},
{'4', '5', '6', '-'},
{'7', '8', '9', 'x'},
{'*', '0', '=', '/'}
};

byte rowPins[ROWS] = {14, 15, 16, 17};
byte colPins[COLS] = {18, 19, 20, 21};

Keypad customKeypad = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);

//Data Setups for inputs
//uses long to allow us to compute larger calculations as specified in manual 
long value;
long* ptr = &value;  //first number pressed by user
long value2;
long* ptr2 = &value2;  //second number pressed by user

//pointer for operation entered, to store which operator is chosen
int state = 0;
int* ptr_state = &state; 
//0 = first number being entered (neutral state - no operation declared yet) 
//1 = addition
//2 = subtraction
//3 = multiplication
//4 = division

char nums[10] = {'1', '2', '3', '4', '5', '6', '7', '8', '9', '0'};
char operation[5] = {'+', '-', 'x', '/', '='};

void setup() {
  Serial.begin(9600);
  lcd.begin(16,2); //setup of lcd with rows, cols of screensize
}

void loop() {
   char customKey = customKeypad.getKey(); 
  
  if (customKey == '*'){ //checking if clear screen is entered
    lcd.clear();
    *ptr = 0;
    *ptr_state= 0; //resets back to 'entering first number' state
  }
  
  for (int i=0; i<10; i++){   //checking if a number is entered FIRST (in neutral state, before operation declared)
    if ((customKey == nums[i]) && (*ptr_state == 0)){
      int new_val = customKey - 48;
    *ptr = *ptr * 10 + new_val;     //multiplies original value by 10 so that when we add the new val, its shifted by one decimal 
    lcd.clear();                      
    lcd.print(*ptr);
    Serial.println("ptr:");
    Serial.println(*ptr);  //points to the entire entered number, & is updated with each new entry
    //Serial.println(new_val);
    }
  }

      //if something that is not a number is entered (an operation)
    if (customKey == operation[0]){ //addition
      *ptr_state = 1; //setting state to addition
      lcd.print('+');
      }

      else if (customKey == operation[1]){ //subtraction
      *ptr_state = 2;
      lcd.print('-');
      }

      else if (customKey == operation[2]){ //multiplication
      *ptr_state = 3;
      lcd.print('x');
        
      }

      else if (customKey == operation[3]){ //division 
      *ptr_state = 4;
      lcd.print('/');
      }

    else if (customKey == operation[4]) { //equal sign
      lcd.setCursor(0,1); //setting cursor to bottom row
      lcd.print("=");
      if (*ptr_state == 1){  //add
        lcd.print(*ptr + *ptr2);
      }

      else if (*ptr_state == 2){ //sub
        lcd.print(*ptr - *ptr2);
      }

      else if (*ptr_state == 3){ //mult
        lcd.print(*ptr * *ptr2);
      }

      else if (*ptr_state == 4){  //divide
        if (*ptr2 == 0){
          lcd.print("Error! Div by 0"); //error if division by zero
        }
        else;
          lcd.print(*ptr / *ptr2);
      }
      *ptr_state = 0; //set state back to zero to input another first number
      *ptr = 0;
      *ptr2 = 0;  //reset pointers
    }    


  for (int i=0; i<10; i++){   //checking if a number is entered
    if ((customKey == nums[i]) && (*ptr_state != 0)){  //checking if num added AFTER an operation is used
      int new_val2 = customKey - 48; 
    *ptr2 = (*ptr2 * 10) + new_val2;  
    lcd.print(new_val2);   
    Serial.println("Ptr2:");
    Serial.println(*ptr2);
    }
  }

  delay(100);  
   }