#include <Keypad.h>
#include <LiquidCrystal_I2C.h>
LiquidCrystal_I2C lcd(0x27,16,2);
const byte rows=4;
const byte cols=4;
int i=0;
String y="12345";
String s="";
String n="";
char keys[rows][cols]={{'1','2','3','A'},{'4','5','6','B'},{'7','8','9','C'},{'*','0','#','D'}};
byte rowpin[rows]={13,12,11,10};
byte colpin[cols]={9,8,7,6};
Keypad des_key= Keypad(makeKeymap(keys),rowpin,colpin,rows,cols);
void setup() 
{
  lcd.clear();
  lcd.init();
  lcd.backlight();
}

void loop() 
{
  char key= des_key.getKey();
  if(key>0)
  {
    switch(key)
    {
      case 'D': changePassword();
      default: checkPassword();
    }
  }
}

void checkPassword()
{
  char key= des_key.getKey();
  if(key>0)
  {
    if(key!='*')
    {
      s=s+key;
      if(key=='#')
      {
        lcd.setCursor(i-1,0);
        lcd.print(" ");
        i=i-1;
        s.remove(i);
      }
      else
      {
        lcd.setCursor(i,0);
        lcd.print("*");
        i=i+1;
      }
    }
    else
    {
      if(y.equals(s))
      {
        lcd.setCursor(0,1);
        lcd.print("Correct Password.");
      }
      else
      {
        lcd.setCursor(0,1);
        lcd.print("Wrong Password.");
      }
    }
  }
}

void resetPassword()
{
  s.remove(0);
  lcd.setCursor(0,0);
  lcd.clear();
}

void changePassword()
{
  lcd.setCursor(0,0);
  lcd.print("Enter password:");
  checkPassword();
  if(y.equals(s))
  {
    resetPassword();
    lcd.setCursor(0,0);
    lcd.print("New Password:");
    delay(1000);
    lcd.clear();
    char key1= des_key.getKey();
    if(key1>0)
    {
      while(key1!='*')
      {
        char key1= des_key.getKey();
        s=s+key1;
        if(key1=='#')
        {
          lcd.setCursor(i-1,0);
          lcd.print(" ");
          i=i-1;
          s.remove(i);
        }
        else
        {
          lcd.setCursor(i,0);
          lcd.print("*");
          i=i+1;
        }
      }  
    }
    n=s;
    lcd.setCursor(0,1);
    lcd.print("Changed.");
    }
  else
  {
    lcd.setCursor(0,0);
    lcd.print("Wrong Input.");
  }
}