Necessary to invoke base-class c'tors; otherwise, the base-class' default
c'tor will be called:
class TeachingAssistant : public Employee
public:
TeachingAssistant(String student_name);
};
TeachingAssistant::TeachingAssistant(String student_name)
// Teaching assistants all get same starting salary
: Employee(student_name, 5000)
{
}