將實現同一功能的多個演算法封裝成多個不同的類，呼叫時更加方便，且避免條件語句的使用。

使用Context類來決定要使用哪個演算法類，使用多型實現。通過在構造Context類時指定哪個演算法類來實現選擇功能。

Strategy類為純虛類，用來派生不同的演算法類。

#include <iostream>
using namespace std;
class Strategy//純虛類 
{
    public:
        virtual ~Strategy(){}
        virtual void AlgorithmInterface()=0;
};
class Context //
 
上下文類 
{
    public:
        Context(Strategy *pStrategy);
        ~Context();
        
        void ContextInterface();
    private:
        Strategy *m_pStrategy; //欄位為指標，記得在解構函式中釋放並置空   
};
Context::Context(Strategy *pStrategy):m_pStrategy(pStrategy)
{
        //上下文建構函式，把演算法賦值給指標 
} 
Context::~Context()
{
    
 
delete m_pStrategy;
    m_pStrategy=nullptr;
}
void Context::ContextInterface()
{
    if(m_pStrategy != nullptr)
    {
        m_pStrategy->AlgorithmInterface();//呼叫對應的演算法 
    } 
} 

class ConcreateStrategyA: public Strategy //策略A 
{
    public:
        virtual ~ConcreateStrategyA(){}
        virtual
 
 void AlgorithmInterface();    
};
void ConcreateStrategyA::AlgorithmInterface()
{
    cout<<"AlgorithmInterface  AAAAA"<<endl;
}

class ConcreateStrategyB: public Strategy //策略B 
{
    public:
        virtual ~ConcreateStrategyB(){}
        virtual void AlgorithmInterface();    
};
void ConcreateStrategyB::AlgorithmInterface()
{
    cout<<"AlgorithmInterface  BBBBB"<<endl;
}
int main(int argc, char *argv[])
{
    //建立一個基類物件指標指向派生類物件 
    Strategy *pStrategy = new ConcreateStrategyA(); 
    //
    Context *pContext = new Context(pStrategy);
     pContext->ContextInterface();
     delete pContext;
    return 0;
}