#include <iostream>using namespace std;class VirtualBase{public:    virtual void Demo() = 0;    virtual void Fun();};void VirtualBase::Fun(){    cout<<"父類的Fun執(zhí)行了"<<endl;}class C:public VirtualBase{public:    void Demo();    void Fun();};void C::Demo(){ cout << "C::Demo!" << endl;}void C::Fun(){ cout << "子類C::Fun!" << endl;}int main(){    cout << "Hello world!" << endl;    //VirtualBase *p = new VirtualBase();   // p->Fun(); //  C c;  // c.Demo();   VirtualBase *p = new C;   p->Demo();   p->Fun();    return 0;}