提供两个十进制数字字符串，并按位计算，模拟竖式计算。可实现超大数相加、相减、相乘（考虑到小数精度问题，除法暂不提供）。运用小学知识编程，最多可计算约 20 亿位数。参数不能为小数、负数、科学计数。-Provide two decimal num strings, and bitwise calculations are performed to simulate vertical calculations. It can be achieved super large number of addition, subtraction, multiplication (taking into account the decimal precision, the division calculation is not provided temporarily). I use of primary knowledge to program, up to calculate about 2 billion digits. Parameters cannot be fractional, negative, scientific count.