1 #include<iostream> 2 using namespace std; 3  4 class base{ 5 public: 6     /*virtual*/ void who(){    //define this function to virtual will be normal 7         cout << "this is the class of base !" << endl; 8     } 9 };10 11 class derive1:public base{12 public:13     void who(){14         cout << "this is the class of derive1 !" << endl;15     }16 };17 class derive2 :public base{18 public:19     void who(){20         cout << "this is the class of derive2 !" << endl;21     }22 };23 int main(){24     base beseObject, *p;25     derive1 obj1;26     derive2 obj2;27     p = &beseObject;28     p->who();29     cout << "------------------------------" << endl;30     p = &obj1;31     p->who();32     ((derive1*)p)->who();33     cout << "------------------------------" << endl;34     p = &obj2;35     p->who();36     ((derive2*)p)->who();37     cout << "------------------------------" << endl;38     obj1.who();39     obj2.who();40     int i;41     cin >> i;42     return 0;43 }

 1 #include<iostream> 2 using namespace std; 3  4 class base{ 5 public: 6     virtual void f1(){    //virtual function 7         cout << "f1 function of base " << endl; 8     } 9     virtual void f2(){    //virtual function10         cout << "f2 function of base " << endl;11     }12     virtual void f3(){    //virtual function13         cout << "f3 function of base " << endl;14     }15     void f4(){    16         cout << "f4 function of base " << endl;17     }18 };19 20 class derive:public base{21 public:22     void f1(){    //virtual function23         cout << "f1 function of derive " << endl;24     }25     virtual void f2(int x){    //lose virtual characteristic26         cout << "f2 function of derive " << endl;27     }28     //f3(){    //wrong, not the same return type29     //    cout << "f3 function of base " << endl;30     //}31     void f4(){    //normal overload32         cout << "f4 function of derive " << endl;33     }34 };35 int main(){36     base obj1, *ptr;37     derive obj2;38     ptr = &obj1;39     ptr->f1();40     ptr->f2();41     ptr->f3();42     ptr = &obj2;43     ptr->f1();44     ptr->f2();45     ptr->f4();46     int i;47     cin >> i;48     return 0;49 }

 1 #include<iostream> 2 using namespace std; 3  4 class base{ 5 public: 6     virtual void print(){ 7         cout << "calss base!" << endl; 8     } 9 };10 class son:public base{11 public:12     virtual void print(){ //empty virtual class13     }14 };15 class grandson :public son{16 public:17     void print(){18         cout << "calss grandson!" << endl;19     }20 };21 void show(base* b){22     b->print();23 }24 int main(){25     base *pbase = new base;26     son *pson = new son;27     grandson *pgrandson = new grandson;28     show(pbase);29     show(pson);30     show(pgrandson);31     int i;32     cin >> i;33     return 0;34 }

 1 #include<iostream> 2 using namespace std; 3  4 class shape{  //抽象类里必须有一个纯虚函数 5 public: 6     virtual float area() = 0; 7 }; 8 class triangle :public shape{ 9 protected:10     float h, w;11 public:12     triangle(float hh, float ww){13         h = hh; w = ww;14     }15     float area(){16         return h*w*0.5;17     }18 };19 class rectangle :public shape{20 protected:21     float h, w;22 public:23     rectangle(float hh, float ww){24         h = hh; w = ww;25     }26     float area(){27         return h*w;28     }29 };30 float total(shape* s[], int n){31     float sum = 0;32     for (int i = 0; i < n - 1; i++)33         sum += s[i]->area();34     return sum;35 }36 int main(){37     shape* s[2];38     s[0] = new triangle(3, 4);39     s[1] = new rectangle(3, 4);40     float sum = total(s, 2);41     cout <<"total area is: "<< sum << endl;;42     int i;43     cin >> i;44     return 0;45 }