Home >Backend Development >C++ >Why Does Integer Math with `pow()` Produce Incorrect Results in C ?

Why Does Integer Math with `pow()` Produce Incorrect Results in C ?

DDD
DDDOriginal
2024-12-04 22:58:11749browse

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!

Statement:
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn