生成一个Rectangle类（长方形），这个类的length和width属性默认取值为1，其成员函数计算长方形的perimeter（周长）和area（面积）。为该类的length和width设置set函数和get函数。set函数应验证length和width均为0.0到20.0之间的浮点数-Generate a Rectangle class (rectangle), the class length and width attribute default value is 1, the members of the function to calculate the rectangle s perimeter (perimeter) and area (area). The length and width for the set of such functions and get the function set. set function should verify the length and width are floating point numbers between 0.0 to 20.0