557: Mainline

Note that a function with a call-by-reference parameter can alter the corresponding argument. The following, for example, would reset a box_car object's percentage_loaded member variable to 100:

void loading_function (box_car& b) { 
  b.percentage_loaded = 100; 
  return; 
} 

The following alternative would not work, because the change would alter only a copy of the argument, rather than the argument itself:

void loading_function (box_car b) {  // DEFECTIVE! 
  b.percentage_loaded = 100; 
  return; 
}