fall thru

fall through
fall thru

   <programming> (The American misspelling "fall thru" is
   also common)

   1. To exit a loop by exhaustion, i.e. by having fulfilled its
   exit condition rather than via a break or exception condition
   that exits from the middle of it.  This usage appears to be
   *really* old, dating from the 1940s and 1950s.

   2. To fail a test that would have passed control to a
   subroutine or some other distant portion of code.

   3. In C, "fall-through" occurs when the flow of execution in a
   {switch statement} reaches a "case" label other than by
   jumping there from the switch header, passing a point where
   one would normally expect to find a "break".  A trivial
   example:

   	switch (colour)
   	{
   	case GREEN:
   	  do_green();
   	  break;
   	case PINK:
   	  do_pink();
   	  /* FALL THROUGH */
   	case RED:
   	  do_red();
   	  break;
   	default:
   	  do_blue();
   	  break;
   	}

   The effect of the above code is to "do_green()" when colour is
   "GREEN", "do_red()" when colour is "RED", "do_blue()" on any
   other colour other than "PINK", and (and this is the important
   part) "do_pink()" __and then__ "do_red()" when colour is "PINK".
   Fall-through is {considered harmful} by some, though there are
   contexts (such as the coding of state machines) in which it is
   natural; it is generally considered good practice to include a
   comment highlighting the fall-through where one would normally
   expect a break.  See also {Duff's Device}.