#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);
  }
}