#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};
char key = '2';

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:
key = keypad.getKey();

delay(100);

if (key>= '0' && key <= '9') {
  Serial.println(key);

} else if(key){
  Serial.println("Please press a number");
}
}