Keypad 4x4

#include <Keypad.h>

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

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

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

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

void setup() {
  Serial.begin(9600);
  while (!Serial) {
    ;
  }
  Serial.println("4x4 Keypad example");
  Serial.println("Press a key on the keypad to see it in the Serial Monitor.");
}

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

  if (key) {
    Serial.print("Key pressed: ");
    Serial.println(key);
  }
}