要求：分别用成员函数和友元函数来求圆的面积和周长。

Requirements: member function respectively, and a friend function to find area and circumference of a circle.

youdao

一个一直没有得到解决的问题是，怎样“求圆的面积”。这个问题的真实意思是：求一个圆的精确面积。

One of the problems that has never been solved is that of "squaring the circle." This really means to find the exact area of a circle.

youdao