Why is my integer math with std::pow giving the wrong answer?

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std::pow() works with floating point numbers, which do not have infinite precision, and probably the implementation of the Standard Library you are using implements pow() in a (poor) way that makes this lack of infinite precision become relevant.

However, you could easily define your own version that works with integers. In C++11, you can even make it constexpr (so that the result could be computed at compile-time when possible):

constexpr int int_pow(int b, int e)
{
    return (e == 0) ? 1 : b * int_pow(b, e - 1);
}

Here is a live example.

Tail-recursive form (credits to Dan Nissenbaum):

constexpr int int_pow(int b, int e, int res = 1)
{
    return (e == 0) ? res : int_pow(b, e - 1, b * res);
}

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