const byte ROWS=4;
const byte COLS=4;

char keys[ROWS] [COLS]={
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};
byte rowPins[ROWS]={9,8,7,6};
byte colPins[COLS]={5,4,3,2};
Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

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

void loop() {
  char key= keypad.getKey();
  if(key){
    Serial.print("Key Pressed : ");
    Serial.println(key);
  }  
}