#include <Keypad.h>
#include <LiquidCrystal_I2C.h>
const byte ROWS = 4; 
const byte COLS = 4; 
int change=1,c=0;
float x=0,y=0,r=0;
char hexaKeys[ROWS][COLS] = {
  {'1', '2', '3', '+'},
  {'4', '5', '6', '-'},
  {'7', '8', '9', '*'},
  {'E', '0', 'C', '/'}
};

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

Keypad customKeypad = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS); 
LiquidCrystal_I2C lcd(0x27, 20 , 4);
void setup(){
  lcd.init();
  lcd.backlight();
}
  
void loop(){
  char customKey = customKeypad.getKey();
  ///input///
  if(customKey)
  {
    if(customKey='E')
      c++;
    if(c=0)
      if(customKey='1')
        x=(x*10)+1;
      if(customKey='2')
        x=(x*10)+2;
      if(customKey='3')
        x=(x*10)+3;
      if(customKey='4')
        x=(x*10)+4;
      if(customKey='5')
        x=(x*10)+5;
      if(customKey='6')
        x=(x*10)+6;   
      if(customKey='7')
        x=(x*10)+7; 
      if(customKey='8')
        x=(x*10)+8;
      if(customKey='9')
        x=(x*10)+9;
      if(customKey='0')
        x=(x*10)+0;
  }
  ////display////
  if(change=1)
  {
    
    if(c=0)
    {
      lcd.setCursor(0,0);
      lcd.print("");
      lcd.print(x);
    }
    if(c=1)
    {
      lcd.setCursor(0,1);
      lcd.print(" ");
      lcd.print(customKey);
    }
    if(c=2)
    {
      lcd.setCursor(0,2);
      lcd.print(" ");
      lcd.print(y);
    }
    if(c=3)
    {
      lcd.setCursor(0,3);
      lcd.print(" ");
      lcd.print("=");
      lcd.print(r);
    }
  }
  delay(50);
}