How to simplyfy switch cases with the same repeating codes but uses different variables

[david_2018]

Serial generally inherits from Stream, so you could do something like this (has not been tested)

void myFunc(int deviceNumber, int x, int y) {
  Stream* serials[] = {
    &Serial1,
    &Serial2,
    &Serial3,
    &Serial4,
    &Serial5,
    &Serial6
  };

  if ((deviceNumber >= 1) && (deviceNumber <= 6)) {
    serials[deviceNumber]->println(x);
    serials[deviceNumber]->println(y);
    serials[deviceNumber]->println(x + y);
  }
}