问题的提出：设计一个用于检查数组在使用时下标是否越界的类，如越界给出提示。（知识点：下标运算符的重载）。-Of the problem: the design of a check for the array subscr ipt in the use of topical whether cross-border class, such as cross-border prompts given. (Knowledge points: subscr ipt operator overloadi