#include<Keypad.h>

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] = {5, 4, 3, 2};
byte colPins[COLS] = {A3, A2, A1, A0};

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

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);

}

void loop() {
  // put your main code here, to run repeatedly:
  delay(100);
  char key = keypad.getKey();
  if (key >= '0' && key <= '9') {
    Serial.println(key);
  }
  else if (key) {
    Serial.println("Please press 1");
  }
}