#include <Keypad.h>
#include <LiquidCrystal.h>

const int ROW_NUM    = 4; // four rows
const int COLUMN_NUM = 4; // four columns
char keys[ROW_NUM][COLUMN_NUM] = {
  {'1','2','3', 'A'},
  {'4','5','6', 'B'},
  {'7','8','9', 'C'},
  {'*','0','#', 'D'}
};
byte pin_rows[ROW_NUM] = {10 ,9, 8, 7};      // connect to the row pinouts of the keypad
byte pin_column[COLUMN_NUM] = {6, 5, 4, 3}; // connect to the column pinouts of the keypad

Keypad customKeypad = Keypad(makeKeymap(keys), pin_rows, pin_column, ROW_NUM, COLUMN_NUM );
const int BUZZER_PIN = 12;

void setup () {
  Serial.begin(9600);
  pinMode(BUZZER_PIN, OUTPUT);
}

void loop () {
  // This is just a snippet from "old" code, to be replaced with the
  // asked basic task of digits input only, then add sound,...
  char customKey = customKeypad.getKey();
  if (customKey) {
    tone(BUZZER_PIN, 750, 100); // make a beep sound
    Serial.print("Enter your PhoneNo.: "); 
    /*if (customKey != NO_KEY) {
      Serial.print(customKey);*/
      char PhoneKey = customKeypad.getKey();
      if (PhoneKey!= NO_KEY) {              
        // Initialize if a key is pressed
          Serial.print(" = ");Serial.println(PhoneKey);
      } 
    }
  }
//}