#include <Keypad.h>

const uint8_t ROWS = 4;
const uint8_t COLS = 4;
char  keys[ROWS][COLS] = {
{'1', '2', '3', 'A', }, 
{'4', '5', '6', 'B', }, 
{'7', '8', '9', 'C', }, 
{'*', '0', '#', 'D', }
};

uint8_t colPins[COLS] = { 5,4,3,2};//pins connected to C1, C2, C3, 
uint8_t rowPins[ROWS] = { 9,8,7,6};//pins connected to R1, R2, R3, 

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

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

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

  if (key != NO_KEY) {
    Serial. println(key) ;
  }
}