Why remainingInvaders is reset to zero (remainingInvaders = 0;) and why add more remainingInvaders

The code you are talking about is not removing or adding invader objects, it is just managing a count.

It sets the count to zero to begin, then checks each invader to see if it is still active. For each one that is, the count is incremented. Then, when the loop ends you have an accurate count of how many invaders are remaining. So you might think of this part of the code as just "taking inventory".

Hi Kevin sorry for late reply,here is the code i am talking about public bool Play() { //run until all invaders are neutralized or an invader reaches the end of the path int remainingInvaders = _invaders.Length;

  while(remainingInvaders > 0)
  {      
      foreach(Tower tower in Towers)
      {
        tower.FireOnInvaders(_invaders);
      }          
      //count and move the invaders that are still active.
      remainingInvaders = 0;
      foreach(Invader invader in _invaders)
      {
          if(invader.IsActive)
          {
              invader.Move();

              if(invader.HasScored)
                  {
                    return false;
                  }              
              remainingInvaders++;
          }
      }
  }
  return true;
}