#include <Keypad.h>
#include <LiquidCrystal_I2C.h>;
byte k;
LiquidCrystal_I2C LCD (0x27 , 16 ,2 );
const uint8_t ROWS = 4;
const uint8_t COLS = 4;
char keys[ROWS][COLS] = {
  { '1', '2', '3', 'A' },
  { '4', '5', '6', 'B' },
  { '7', '8', '9', 'C' },
  { '*', '0', '#', 'D' }
};

uint8_t colPins[COLS] = { 5, 4, 3, 2 }; // Pins connected to C1, C2, C3, C4
uint8_t rowPins[ROWS] = { 9, 8, 7, 6 }; // Pins connected to R1, R2, R3, R4

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

void setup() {
  Serial.begin(9600);
  LCD.init();
  LCD.backlight();
  LCD.setCursor(0,0);
  LCD.print("Enter code");
  LCD.setCursor(0,1);
}

void loop() {
  char key = keypad.getKey();

  if ((k<6)&& (key != NO_KEY)&&(key>='0')&&(key<='9')) 
  { 
    Serial.println(key);
    LCD.print(key);
    k++;
  }
  if(key=='A')
  {
   LCD.setCursor(0,1);
   LCD.print("       ");
   LCD.setCursor(0,1);
   k=0;
  }
  if((key=='B')&&(k>0))
  {
   LCD.setCursor((k-1),1);
   LCD.print(" ");
   LCD.setCursor((k-1),1);
   k--;
  }
}