实现一个三维点(x,y,z)的Point类。包含一个构造函数，一个复制构造函数，一个把这个点变成负的函数negate( )，一个返回到(0,0,0)点的距离的函数norm( )和一个print( )函数。

（1）为类Point实现一个重载的赋值运算符。

（2）为类Point实现重载的流插入运算符。

（3）为类Point实现重载的比较关系运算符==和!=。

（4）为类Point实现重载的加法+和减法运算符-。

（5）实现一个重载的乘法运算符*来返回两个Point类对象的点积。

-To achieve a three-dimensional point (x, y, z) of the Point class. Contains a constructor, a copy constructor, this point becomes a negative function negate (), a return to the (0,0,0) of a function of the distance norm (), and a print () function. (1) class Point to achieve an overloaded assignment operator. (2) class Point to achieve overloaded stream insertion operator. (3) Comparison of class Point to achieve overloaded relational operators == and! =. (4) To achieve the overloaded class Point addition+ and subtraction operator-. (5) to achieve an overloaded multiplication operator* to return two Point class object of the dot product.