try this.c

int result = 0;

void loop() {
  char key = kpd.getKey();
  if(key)  // Check for a valid key.
  {
    switch (key)
    {
      case '*':
        result = 0;
        break;
      case '#':
        result = 0;
        break;
      default:
        result = result * 10 + toInt(key)
        Serial.println(result);
    }
  }
}