Bignum

realize the overloading of basic operators(+ - * / >> <<);
compile the demo with instructions : g++ -o a.exe main.cpp Bignum.cpp;
and run it with the instructions : a.exe input_file_path output_file_path
which input_file_path is the path of input file and the other is output file.
but there must be a space between numerals and operators (like that : 123 + 456)