#include <Keypad.h>

String password = "1234DA";
String input = "";

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] = { 16, 4, 2, 15 };
uint8_t rowPins[ROWS] = { 19, 18, 5, 17 };

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

void setup() {
  Serial.begin(9600);
  Serial.print("Enter password: ");
}

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

  if (key) {
    if (key == '#'){
      Serial.println("");
      if (input.compareTo(password) == 0){
        input = "";
        Serial.print("Access Granted");
        while(true);
      }
      else{
        Serial.println("Access Denied");
        Serial.print("Try Again");
        input = "";
      }
    }
    else if (key == '*'){ // clear the input 
    string input = ""; 
    Serial.println(); 
    Serial.print("Password cleared, enter again : "); 
    }
      else{
        input.concat(key);
        Serial.print(key);
      }
    }
  }