128: Mainline

In the following program, box_car_volume is redefined, yet again, albeit awkwardly, to illustrate the limited availability of parameter values:

#include  
// Define multiplier and box_car_volume first: 
double multiplier ( ) { 
  return h * w * l;                                     // BUG! 
} 
double box_car_volume (double h, double w, double l) { 
  return multiplier ( ); 
} 
// Then, define main: 
main ( ) { 
  cout << "The volume of the box car is " 
       << box_car_volume (10.5, 9.5, 40.0) << endl; 
  cout << "The value of the parameters are " 
       << h << ", " << w << ", and " << l               // BUG! 
       << endl; 
} 

In this program, box_car_volume asks multiplier—a function with no parameters—to perform the actual computation of h * w * l. However, the C++ compiler cannot compile multiplier, because no values for the h, w, or l parameters of box_car_volume are available to multiplier.

Moreover, C++ cannot compile the second output statement in the main function. The reason is that h, w, and l exist only during the execution of the function in which they appear as parameters; h, w, and l no longer exist once that function has returned.