#include <Keypad.h>
const byte ROWS=4;
const byte COLS=4;
byte colPins[COLS]={7,8,9,10};
byte rowPins[ROWS]={3,4,5,6};
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};
Keypad cde = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);
void setup() {
Serial.begin(9600);
}

void loop() {
char customKey=cde.getKey();
if(customKey){
  Serial.println(customKey);
}
}