#include <Keypad.h>
const uint8_t row = 4;
const uint8_t column = 4;

char keys[row][column] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

uint8_t columns[column] = {5, 4, 3, 2};
uint8_t rows[row] = {9, 8, 7, 6};

Keypad keypad = Keypad( makeKeymap(keys), rows, columns, row, column);

String text = "";
void setup() {
  Serial.begin(9600);
}

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

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