c - 浮点乘法在 C 中的意外输出

Question

我在 C 中执行乘法和加法运算，但得到了错误的结果。

我正在执行以下操作:

#include <stdio.h>
#include <strlib.h>
#include <math.h>

int main() 
{
    float** fpimag;
    float** fpreal;

    // Some code to assign fpimag and fpreal
    // fpimag and fpreal are two dimensional arrays that are
    // passed by reference to some functions to assign data to them
    allocatememory(&fpimag,&fpreal);
    storedata(&fpimag,&fpreal);


    autofunction(&fpimag,&fpreal);
} // main()

void autofunction(float*** fpimag,float***fpreal) {
    float expreal;
    float expimag;

    expreal = cos((*afph_correct)[row][column]);
    expimag = sin((*afph_correct)[row][column]);

    (*fpimag)[row][column] = (*fpimag)[row][column] * expreal + (*fpreal)[row][column] * expimag;

 printf("Operation looks like this\n");
 printf("%f*%f + %f*%f\n",(*fpimag)[row][column],expreal,(*fpreal)[row][column],expimag);
 printf("The value is %f\n",(*fpimag)[row][column]);
} // autofunction

这是我得到的输出:

Operation looks like this
-0.003095*-0.431162 + 0.000027*-0.902275
The value is 0.003865

然而正确答案应该是:

0.0013101

谢谢!

Answer 1

试试 long double，比 float 更精确: http://en.wikipedia.org/wiki/Long_double

请注意，您应该更改您的 printf(%Lf 表示 long double)