class中变量默认是private，struct中的变量默认是public，其他两个均相似，可以有构造函数析构函数，也可以继承。#include 
     
      using namespace std;enum BREED {GOLDEN,CAIRN,DANDIE,SHETLAND,DOBERMAN,LAB};struct Mammal{    public:        Mammal():itsAge(2),itsWeight(5){}        ~Mammal() {}        int GetAge() const {return itsAge;}        void SetAge(int age) {itsAge = age;}        int GetWeight() const {return itsWeight;}        void SetWeight(int weight) {itsWeight = weight;}        void Speak() const {cout<<"\nMammal sound!";}        void Sleep() const {cout<<"\nShhh.I'm sleeping.";}    protected:        int itsAgel;        int itsWeight;               }; struct Dog:public Mammal{    public:        Dog():itsBreed(GOLDEN){}        ~Dog(){}        BREED GetBreed() const {return itsBreed;}        void SetBreed(BREED breed) {itsBread = breed;}        void WagTail() const {cout<<"Tail wagging...\n";}        void BegForFood() const {cout<<"Begging for food...\n";}    private:        BREED itsBreed;       };int main(){    Dog fido;    fido.Speak();    fido.WagTail();    cout<<"Fido is"<
      
       <<"years old \n";    return 0;      }