Arduino code 4x4 Keypad Robojax.com

This is the Arduino code for 4x4 keypad.

This video shows you how to use 4x4 keypad for arduino. http://robojax.com/learn/arduino/
  1. Library code for 4x4 Keypad

 /*
 * Original sourse: https://playground.arduino.cc/Code/Keypad
 * This is the Arduino code for 4x4 keypad.
 * watch the video for details and demo http://youtu.be/qIDzzG2LUtg
 *  * 
 * Written by Ahmad Nejrabi for Robojax Video channel www.Robojax.com
 * Date: Dec 18, 2017, in Ajax, Ontario, Canada
 * Permission granted to share this code given that this
 * note is kept with the code.
 * Disclaimer: this code is "AS IS" and for educational purpose only.
 * this code has been downloaded from http://robojax.com/learn/arduino/
 * 
 */
/* @file HelloKeypad.pde
|| @version 1.0
|| @author Alexander Brevig
|| @contact alexanderbrevig@gmail.com
||
|| @description
|| | Demonstrates the simplest use of the matrix Keypad library.
|| #
*/
#include <Keypad.h>

const byte ROWS = 4; //four rows
const byte COLS = 4; //three columns
char keys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};

byte rowPins[ROWS] = {2, 3, 4, 5}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {6,7,8,9}; //connect to the column pinouts of the keypad

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

void setup(){
  Serial.begin(9600);
}
  
void loop(){
  char key = keypad.getKey();
    // just print the pressed key
   if (key){
    Serial.println(key);
  } 
  
  // this checkes if 4 is pressed, then do something. Here  we print the text but you can control something.
  if (key =='4'){
    Serial.println("Key 4 is pressed");
  }
}