对一些超出整型数范围的正整数的应用，需要自己想办法解决的存储和运算。一种解决方案是用单链表存储一个正整数。注意，数字是用逆序存储的。试设计一个类处理任意大整数，必须实现输入输出操作、加法操作和赋值操作。(For some applications that are beyond the integer range of positive integers, they need to store and compute their own solutions. One solution is to