定义一个复数类Complex，包含2个私有成员double real,imaginary，分别表示复数的实部和虚部。请定义出复数类的构造函数，同时重载以下函数：

 　　重载加法（+）为复数加上对象，作为类的成员函数。

 　　重载减法（-）为复数减去实数，作为类的友元函数。

-Definition of a complex number class Complex, individual and private member includes two double real, imaginary, respectively, the real part and imaginary part. Please define complex class constructor, while overloading the following functions: 　overloaded Addition (+) plus the object is complex, as the class member functions. 　overloaded subtraction (-) minus the real number is a complex number, as the class friend function.