How to sum large numbers?

Question

I am trying to calculate 1 + 1 * 2 + 1 * 2 * 3 + 1 * 2 * 3 * 4 + ... + 1 * 2 * ... * n where n is the user input. It works for values of n

Answer 1

You could use a double, especially if your platform uses IEEE754.

Such a double gives you 53 bits of precision, which means integers are exact up to the 53rd power of 2. That's good enough for this case.

If your platform doesn't use IEEE754 then consult the documentation on the floating point scheme adopted. It might be adequate.