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

#define ROWS 4
#define COLS 4
#define BT_DEL 6

char operation;
String n1;
String n2;

uint8_t rowPins[4] = {2, 3, 4, 5};
uint8_t colPins[4] = {A5, A4, A3, A2};

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

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

LiquidCrystal lcd(12, 11, 10, 9, 8, 7);

void intro(){
  lcd.setCursor(3, 0);
  lcd.print("Arduino Cal");
  delay(200);
  lcd.setCursor(5, 1);
  String men = "Thauas";
  for (byte i = 0; i < men.length(); i++) {
    lcd.print(men[i]);
    delay(50);
  }
  delay(2100);
  lcd.clear();
}

void setup() {
  pinMode(BT_DEL, INPUT_PULLUP);
  lcd.begin(16, 2);
  intro();
}

float calculate(float n1, float n2, char s){
  switch(s){
    case '+':
      return n1+n2;
    case '-':
      return n1-n2;
    case '*':
      return n1*n2;
    case '/':
      return n1/n2;
  }
}

void loop() {
  char key = keypad.getKey();
  if(digitalRead(BT_DEL) == LOW){
    n1 = "";
    n2 = "";
    operation = '\0';
    lcd.clear();
  }
  if(key != NO_KEY){
    if(key == '+' || key == '-' || key == '*' || key == '/'){
      if(n1.length() > 0){
        lcd.setCursor(0, 1);
        operation = key;
        lcd.print(operation); 
      }
    }
    else if(key != '='){
      if(operation == 0){
        if(n1.length() == 0 && key == '.'){}
        else{
          n1 += key;
          lcd.clear();
          lcd.setCursor(1, 0);
          lcd.print(n1);
        }
      }
      else{
        if(n2.length() == 0 && key == '.');
        else{
          n2 += key;
          lcd.clear();
          lcd.setCursor(1, 0);
          lcd.print(n1);
          lcd.setCursor(0, 1);
          lcd.print(operation);
          lcd.print(n2);
        }
      }
    }
    else{
      if(operation != 0 && n1.length() > 0 && n2.length() > 0){
        lcd.clear();
        float result = calculate(n1.toFloat(), n2.toFloat(), operation);
        n1 = String(result);
        n2 = "";
        operation = '\0';
        lcd.print(result);
      }
    }
  }
}