Home >Backend Development >C++ >Why Does Integer Math with `pow()` Produce Incorrect Results in C ?
Integer Math with pow() Leading to Incorrect Results
Consider the following code snippet:
int i = 23; int j = 1; int base = 10; int k = 2; i += j * pow(base, k); cout << i << endl;
Expectedly, this code should output "123," but instead, it surprisingly prints "122." This unexpected result may baffle you, especially if you're compiling with g 4.7.2 in a Windows XP environment.
At the heart of this discrepancy is the fact that std::pow() is designed to handle floating-point numbers. While these floating-point numbers offer convenience, they come with a trade-off: limited precision. In the case of std::pow(), the implementation may not handle exponentiation with perfect accuracy, leading to rounding errors.
To address this issue, one could harness the power of C 11 and define their own integer exponentiation function:
constexpr int int_pow(int b, int e) { return (e == 0) ? 1 : b * int_pow(b, e - 1); }
This custom int_pow function is tailored specifically for integers, ensuring accurate results.
Alternatively, a tail-recursive approach proposed by Dan Nissenbaum is also a viable solution:
constexpr int int_pow(int b, int e, int res = 1) { return (e == 0) ? res : int_pow(b, e - 1, b * res); }
With these options at hand, you can now confidently wield integer exponentiation in your C programs, banishing incorrect results to the realm of forgotten bugs.
The above is the detailed content of Why Does Integer Math with `pow()` Produce Incorrect Results in C ?. For more information, please follow other related articles on the PHP Chinese website!