#include <Keypad.h>
const byte ROWS = 4;
const byte COLS = 4;

char hexaKeys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};
byte rowPins[ROWS] = {11, 10, 9, 8}; 
byte colPins[COLS] = {7, 6, 5, 4}; 

Keypad customKeypad = Keypad( makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS); 

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

void loop(){
  char customKey = customKeypad.getKey();
  if (customKey){
    Serial.println(customKey);
  }
}