为什么乘两个大的双数给出错误的结果？ [英] Why does multiplying two large double numbers give a wrong result?

问题描述

此双乘法（双）1000000007 *（双）11111111的输出应以7（或等于11111111077777777精确）结束。但我写的这段代码输出结果以6（或等于11111111077777776要精确）。我不知道我可能做错了什么。任何帮助将是巨大的。

The output for this double multiplication (double)1000000007 * (double)11111111 should end with 7 (or equal to 11111111077777777 be precise). But this piece of code I wrote outputs the result ending with 6 (or equal to 11111111077777776 to be precise). I cannot figure out what I might be doing wrong. Any help would be great.

#include <iostream>
#include <iomanip>

using namespace std;

int main()
{
    cout << setprecision(40) << (double)1000000007 * (double)11111111;
}

推荐答案

code> double 值，结果不准确。 double 有一个固有的精度，虽然相当准确，但不够准确，不足以代表您的价值。

When you do multiplication with double values, the results are not precise. There is an inherent precision available to double, which, while fairly accurate, is not precise enough to exactly represent your value.

我建议您阅读每个计算机科学家应该知道的浮点运算。

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