定义一个正方形(square)类，该类包括：正方形的边长(length)(取值范围(range)为1-30个"*")，四个成员函数，分别为：取边长、设置边长、画正方形和在构造这些类对象时能初始化正方形边长。- Defines square (square) the class, this kind includes: Square length of side (length) (value scope (range) is 1-30 "* "), four member functions,