#include <LiquidCrystal.h> // include the LCD library
#include <Keypad.h> // include the keypad library

// initialize the LCD display
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

// initialize the keypad
const byte ROWS = 4; // number of rows on the keypad
const byte COLS = 4; // number of columns on the keypad
char keys[ROWS][COLS] = { // define the keypad layout
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};
byte rowPins[ROWS] = {9, 8, 7, 6}; // connect the row pins of the keypad to these Arduino pins
byte colPins[COLS] = {13, 10, A0, A1}; // connect the column pins of the keypad to these Arduino pins
Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS ); // initialize the keypad with the defined layout and pins

// define the fixed pin
const int fixedPin = 1234; // change this to your desired fixed pin

void setup() {
  // initialize the LCD display
  lcd.begin(16, 2);
  // print a welcome message on the LCD
  lcd.print("Welcome!");
  // set the cursor to the second line
  lcd.setCursor(0, 1);
  // print instructions on the LCD
  lcd.print("Enter pin:");
}

void loop() {
  // get input from the keypad
  char key = keypad.getKey();
  // check if a key is pressed
  if (key) {
    // check if the key is a number
    if (key >= '0' && key <= '9') {
      // add the number to the pin
      int pin = key - '0';
      // print the number on the LCD
      lcd.print(key);
      // wait for 500 milliseconds
      delay(500);
    }
    // check if the key is the special character
    else if (key == 'A' || key == 'B' || key == 'C' || key == 'D') {
      // check if the entered pin is correct
      if (pin == fixedPin) {
        // print the special character on the LCD
        lcd.print("!");
        // wait for 500 milliseconds
        delay(500);
      }
      else {
        // print an error message on the LCD
        lcd.print("Incorrect pin!");
        // wait for 500 milliseconds
        delay(500);
        // clear the LCD display
        lcd.clear();
        // print instructions on the LCD
        lcd.print("Enter pin:");
      }
    }
  }
}

// This code was adapted from the following sources:
// - LiquidCrystal library examples: https://www.arduino.cc/en/Reference/LiquidCrystal
// - Keypad library examples: https://www.arduino.cc/en/Tutorial/Keypad