定义一个圆类（Circle），属性为半径（radius），要求用友元函数来求圆的面积和周长。-definition of a category yen (Circle), the properties of the radius (radius). UF yuan function request to seek a round of the area and perimeter.

特色按钮,传统的矩形按钮改变为其他按钮的形状.-Feature button, the button changes the traditional rectangular shape of the button for other,