//for
// https://forum.arduino.cc/t/help-creating-a-space-invaders-game/1056886
// wokwi: https://wokwi.com/projects/349068891377369684

# define WIDTH  7

int virtualColmRowToRealN(int virtualColm, int virtualRow)
{
  int realN;

  realN = virtualRow / 2;      // full double rows
  realN = realN * WIDTH * 2;   // add double width

// then fix the column in

  if (virtualRow & 0x1) { // odd rows
    realN += WIDTH * 2 - virtualColm - 1;
  }
  else { // even rows
    realN += virtualColm;
  }

// or use the teneray operator instead of if/else
//  realN += (virtualRow & 0x1) ? ( WIDTH * 2 - virtualColm - 1) : virtualColm;

  return realN;
}

void setup() {
  Serial.begin(115200);
  Serial.println("hello maths workd!\n");

  for (int row = 0; row < WIDTH; row++) {
    for (int colm = 0; colm < WIDTH; colm++) {

      Serial.print(virtualColmRowToRealN(colm, row));
      Serial.print("   ");
    }
    Serial.println("");
  }
}

void loop() {
  // put your main code here, to run repeatedly:
}