C ++将负整数与正整数相除会得到正数结果

如何解决C ++将负整数与正整数相除会得到正数结果

我被分配去使用NUCLEO F401RE开发板进行程序设计班的一个小项目。我选择使用Mbed studio进行编程，因为我认为它比在STM32 Cude IDE上编程更容易。但是，我遇到一个问题，有时将负浮点数与正整数相除时，结果却是正数。我决定编写一个程序来测试上述划分。

#include "mbed.h"

// main() runs in its own thread in the OS
int main()
{
    int i = 1;
    while (true) {
        printf("Divided by %d : %f\n",i,-21.837046/i++);
    }
}

这是前40次迭代的结果

Divided by 1 : -21.837047
Divided by 2 : -10.918524
Divided by 3 : -7.279016
Divided by 4 : -5.459262
Divided by 5 : -4.367410
Divided by 6 : -3.639508
Divided by 7 : -3.119579
Divided by 8 : -2.729631
Divided by 9 : -2.426339
Divided by 10 : -2.183705
Divided by 11 : -1.985187
Divided by 12 : -1.819754
Divided by 13 : -1.679773
Divided by 14 : -1.559790
Divided by 15 : -1.455804
Divided by 16 : -1.364816
Divided by 17 : -1.284533
Divided by 18 : -1.213170
Divided by 19 : -1.149319
Divided by 20 : -1.091853
Divided by 21 : -1.039860
Divided by 22 : 0.992594
Divided by 23 : 0.949437
Divided by 24 : 0.909877
Divided by 25 : 0.873482
Divided by 26 : 0.839887
Divided by 27 : 0.808780
Divided by 28 : 0.779895
Divided by 29 : 0.753002
Divided by 30 : 0.727902
Divided by 31 : 0.704421
Divided by 32 : 0.682408
Divided by 33 : 0.661729
Divided by 34 : 0.642267
Divided by 35 : 0.623916
Divided by 36 : 0.606585
Divided by 37 : 0.590191
Divided by 38 : 0.574660
Divided by 39 : 0.559925
Divided by 40 : 0.545927

请注意，从i = 1到i = 21，结果为预期的负数，但是当i> = 22时，结果为正数。有趣的是，当我将分子更改为不同的数字（例如-30）时，结果在i> = 31时从负数转换为正数。不同的分子具有不同的i值，结果在其中转移。

Divided by 1 : -30.000000
Divided by 2 : -15.000000
Divided by 3 : -10.000000
Divided by 4 : -7.500001
Divided by 5 : -6.000000
Divided by 6 : -5.000000
Divided by 7 : -4.285715
Divided by 8 : -3.750001
Divided by 9 : -3.333334
Divided by 10 : -3.000000
Divided by 11 : -2.727273
Divided by 12 : -2.500001
Divided by 13 : -2.307693
Divided by 14 : -2.142858
Divided by 15 : -2.000000
Divided by 16 : -1.875001
Divided by 17 : -1.764706
Divided by 18 : -1.666667
Divided by 19 : -1.578948
Divided by 20 : -1.500001
Divided by 21 : -1.428572
Divided by 22 : -1.363637
Divided by 23 : -1.304348
Divided by 24 : -1.250001
Divided by 25 : -1.200000
Divided by 26 : -1.153847
Divided by 27 : -1.111112
Divided by 28 : -1.071429
Divided by 29 : -1.034483
Divided by 30 : -1.000000
Divided by 31 : 0.967742
Divided by 32 : 0.937501
Divided by 33 : 0.909091
Divided by 34 : 0.882353
Divided by 35 : 0.857143
Divided by 36 : 0.833334
Divided by 37 : 0.810811
Divided by 38 : 0.789474
Divided by 39 : 0.769231
Divided by 40 : 0.750001