Hi!
One of the C++ programmers problems is to save integers more than 2^64-1(we can save 0 to 2^64-1 in unsigned long long int).
It is the best bignum I ever have seen: Link.
It has operations:
+,-,/,*,%,^(pow) ,gcd,lcp,abs.Can work with ostream(cout), istream(cin).
Can convert to
long long,string.It uses fast multiplication.




