c++类与对象，编写一个类

//活太多了，就写一个函数吧。未测试
class A
{
private:
    int*arr;
    int size;//长度
public:
    A(int length=10){arr=new int[length];size=length;}
    ~A(){delete arr;}
    extent(int difference);
}
A::extent(int difference)
{
    int*tmp=arr;
    int size_new=size+difference;
    arr=new int[size_new];
    int min=size_new<size?size_new:size;
    for(int i=0;i<min;i++)
    {
        arr[i]=tmp[i];
    }
    delete tmp;
}