Given the following classes, implement a default constructor and the necessary copy - control members.
对于如下的类, 实现默认构造函数和必要的 复制控制 成员.
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Description of the copy - control behavior of classes that mimic the way arithmetic types are copied.
对类模拟算术类型复制方式的复制控制控制行为的描述.
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A value like class that has a pointer member must define its own copy - control members.
具有指针成员的值型类必须定义自己的 复制控制 成员.
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