#include <Keypad.h>

byte rowpin[4]={2,3,4,5};
byte colpin[4]={6,7,8,9};

char keys[4][4] = {
  {"1","2","3","A"},
  {"4","5","6","B"},
  {"7","8","9","C"},
  {"*","0","#","D"}
  };
  
Keypad N=Keypad(makeKeymap(keys),rowpin,colpin,4,4);
void setup() {
  Serial.begin(9600);
}

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

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