#include <Keypad.h>

const unit8_t ROW=4;
const unit8_t cols=4;
char keys[ROWS][COLS]={
{ '1','2','3','A' },
{ '4','5','6','B' },
{ '7','8','9','C' },
{ '*','0','#','D' }
};

unit8_t colPins[COLS]={5,4,3,2};
unit8_t rowPins[ROWS]={9,8,7,6};

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);
  }
}