#include <Key.h>
#include <Keypad.h>

const byte ROWS = 4; 
const byte COLS = 4;

byte rowPins[ROWS] = {5, 4, 3, 2}; // Array definition.
byte colPins[COLS] = {6, 7, 8, 9};

char buttons[ROWS][COLS] = {
     {'1', '2', '3', 'A'}, // 1st row
     {'4', '5', '6', 'B'}, // 2nd row
     {'7', '8', '9', 'C'}, // 3rd row
     {'*', '0', '#', 'D'} // 4th row
}; // 2D array of character type variables.

Keypad pad = Keypad(makeKeymap(buttons), rowPins, colPins, ROWS, COLS); // create an instance (with name pad) of the object Keypad, which is made available by the Keypad library.


void setup() {
  // put your setup code here, to run once:
     // Initialize Serial Monitor:
     Serial.begin(9600);
}


void loop () {
  // put your main code here, to run repeatedly:
     char result = pad.getKey();
     
     if (result) { // if result is non-zero; could also put (result!=0)
          Serial.println(result);
     }
}