502: Mainline

Once display_capacity is defined in the railroad_car, box_car, and tank_car classes, you can add it to the for loop:

// Display classes using display_short_name virtual function:
for (n = 0; n < car_count; ++n) {
  train[n] -> display_short_name ( );
  cout << "     ";
  train[n] -> display_capacity ( );  
  cout << endl; 
}