The megaint class can store an arbitrarily large integral number, similarly to the Integer type in haskell. It can do addition, subtraction, multiplication, exponentiation, and can be output to a stream.
megaint a(10);
megaint b(30);
megaint c = a * b; // 300
megaint d = a + b; // 40
megaint e = a - b; // -20
megaint f = a^b; // 1000000000000000000000000000000
megaint is pretty basic. It simply stores a vector of type bool, where each bool is a bit in the number. That is, megaint runs on base 2.