# include <Keypad.h>

const byte FILAS = 4; // asignamos variables FILAS, const byte es una variable solo para 8 byte
const byte COLUMNAS = 4;

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

byte pinesFilas[FILAS] = {11,10,9,8};
byte pinesColumnas[COLUMNAS] = {7,6,5,4};

Keypad teclado = Keypad(makeKeymap(keys), pinesFilas, pinesColumnas, FILAS, COLUMNAS);
char key;

void setup(){
  Serial.begin(9600);
}

void loop(){
  key = teclado.getKey();
  if(key){
    Serial.println(key);
  }
}