#include <vector>
#include <iostream>

using namespace std;

class Behaviour
{
public:
    Behaviour() = default;
    virtual ~Behaviour() = default;

    virtual int apply(int target) = 0;
};

class Add : public Behaviour
{
public:
    Add(int value) : value{value}
    {}
    
    virtual int apply(int target) override
    {
	return target += value;
    }
    
private:
    int value;
};

class Square : public Behaviour
{
public:
    Square()
    {}

    virtual int apply(int target) override
    {
	return target * target;
    }
};

int main()
{   
    int value{0};
    Add a1{3};
    Square s1{};
    Add a2{1};
    Square s2{};
    std::vector<Behaviour*> behaviours { &a1, &s1, &a2, &s2 };
    
    for ( Behaviour* behaviour_pointer : behaviours )
    {
	value = (*behaviour_pointer).apply(value);
    }
    std::cout << value << std::endl;
}