#include <iostream>
#include <vector>

using namespace std;

class Animal {
    public:
        virtual void talk();
};

class Duck : public Animal {
    public:
        void talk() { cout << "quack" << endl; }
};

class Horse : public Animal {
    public:
        void talk() { cout << "neigh" << endl; }
};

int main(){
    vector<*Animal> animals;
    animals.push_back(new Duck());
    animals.push_back(new Horse());
    for(auto i = animals.begin(); i != animals.end(); i++){
        Animal* a = *i;
        a->talk();
    }
}
/*
λ g++ main.cpp -o main
main.cpp: In function 'int main()':
main.cpp:22:13: error: '*' cannot appear in a constant-expression
     vector<*Animal> animals;
             ^
main.cpp:22:19: error: template argument 1 is invalid
     vector<*Animal> animals;
                   ^
main.cpp:22:19: error: template argument 2 is invalid
main.cpp:23:13: error: request for member 'push_back' in 'animals', which is of non-class type 'int'
     animals.push_back(new Duck());
             ^
main.cpp:24:13: error: request for member 'push_back' in 'animals', which is of non-class type 'int'
     animals.push_back(new Horse());
             ^
main.cpp:25:14: error: 'i' does not name a type
     for(auto i = animals.begin(); i != animals.end(); i++){
              ^
main.cpp:25:35: error: expected ';' before 'i'
     for(auto i = animals.begin(); i != animals.end(); i++){
                                   ^
main.cpp:25:35: error: 'i' was not declared in this scope
main.cpp:25:48: error: request for member 'end' in 'animals', which is of non-class type 'int'
     for(auto i = animals.begin(); i != animals.end(); i++){
*/