用双向链表实现任意位数的正负整数或小数的加法、减法和乘法运算以及对文件的相关操作。

文件说明：

给定的文件a*.txt为第一个数，b*.txt为第二个数，要求加法产生的结果存储在add*.txt中，减法产生的结果存储在sub*.txt中，乘法产生的结果存储在mult*.txt中，*为对应的一组数据。

-The realization of arbitrary list with two-way median of positive and negative integers or decimal addition, subtraction and multiplication, as well as documents related to the operation. Document Descr iption: given a*. txt file as the first number, b*. txt for the second number, the result of requests adder is stored in the add*. txt, the subtraction result is stored in the sub*. txt in , multiply the result is stored in the mult*. txt, the* for the corresponding one set of data.