c++复习：类

一、不能被继承的类

构造函数析构函数定义为 private

public中定义static函数调用构造函数析构函数

class Sealed_classes
{
    public:
        static Sealed_classes* getnew()
        {
            return new Sealed_classes();
        }
        static void delete_new(Sealed_classes clss)
        {
            delete clss;
        }
    private:
        Sealed_classes(){}
        ~Sealed_classes(){}
};

二、不用*/、循环、条件判断求1+2+...+n的和

使用构造函数+static实现求和

class Tmp
{
public:
    Tmp(){N++;sum+=N;}
    static void reset(){N=0;sum=0;}
    static int get_sum(){return sum;}
private:    
    static int N;
    static int sum;
};

int main()
{
    Tmp::reset();
    Tmp *a=new tmp[n];
    delete []a;
    a=NULL;
    return Tmp::get_sum();
}