#include <Keypad.h>

#define row_num 4
#define col_num 4

String password = "111111";
String input = "";

char keys[row_num][col_num] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'},
};
byte row_pins[row_num] = {19, 18, 5, 17};
byte col_pins[col_num] = {16, 4, 2, 15};

Keypad keypad = Keypad(makeKeymap(keys), row_pins, col_pins, row_num, col_num);

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);
  Serial.print("Enter password: ");
}

void loop() {
  // put your main code here, to run repeatedly:
  char key = keypad.getKey();
  if (key){
    if(key == '#'){
       Serial.println();

       if(input.compareTo(password) == 0){
        Serial.println("Access Granted, Welcome!");
        while(true);
       }
       else{
        Serial.println("Access Denied!");
        Serial.print("Try Again: ");
       }

       input="";
    }
    else if(key == '*'){
      input ="";
      Serial.println();
      Serial.print("Password cleared, enter again: ");
    }
    else{
      input.concat(key);
      Serial.print(key);
    }
  }
}