不要忘记最后那个 default 分支

不要忘记最后那个 default 分支。

即使程序真的不需要 default 处理， 也应该保留语句 default : break; 这样做并非多此一举，而是为了防止别人误以 为你忘了 default 处理。

 #include <iostream>

 /* run this program using the console pauser or add your own getch, system("pause") or input loop */
 using namespace std;
 //定义有两个虚函数的基类
 class Base {
 public:
     //定义两个虚函数
     virtual void aFn1(void){
         cout<<"aFnl is in Base class."<<endl;
     }
     virtual void aFn2(void) {
         cout<<"aFn2 is in Base class."<<endl;
     }
     //定义非虚函数
     void aFn3(void) {
         cout<<"aFn3 is in Base class."<<endl;
     }
 };

 //派生类Derived_1中重新定义了基类中的虚函数aFn1
 class Derived_1:public Base
 {
 public:
     void aFn1(void) {   //覆盖aFn1()函数
         cout<<"aFnl is in First derived class."<<endl;
     }
     // void aFn3(void) {   语法错误
     //    cout<<"aFn3 is in First derived class."<<endl;
     //}
 };

 //派生类Derived_2中重新定义了基类中的虚函数aFn2
 class Derived_2:public Base{
 public:
     void aFn2(void){   //覆盖aFn2()函数
         cout<<"aFn2 is in Second derived class."<<endl;
     }
     // void aFn3(void) {   语法错误
     //    cout<<"aFn3 is in Second derived class."<<endl;
     //}
 };
 //main()函数的定义

 int main(int argc, char** argv) {

     //创建和使用基类Base的对象
     Base b;
     cout<<"Base:"<<endl;
     b.aFn1();
     b.aFn2();
     b.aFn3();
     cout<<"----------------------"<<endl;

     //创建和使用派生类Derived_1的对象
     Derived_1 d1;
     cout<<"Derived_1:"<<endl;
     d1.aFn1();
     d1.aFn2();
     d1.aFn3();
     cout<<"----------------------"<<endl;

     //创建和使用派生类Derived_2的对象
     Derived_2 d2;
     cout<<"Derived_2:"<<endl;
     d2.aFn1();
     d2.aFn2();
     d2.aFn3();
     return ;
 }