1.#QNAN0 output when calculating standard deviation C

问题

I've written a function for calculating the standard deviation and the result is always '1.#QNAN0', I've tried formatting it in different ways but I can't find a solution. It was working on a different computer yesterday, is there anything I can do?

void CalcStandardDeviation(int count, int* nums, double mean, FILE* output){
    int k;
    double std=0,a;
    for (k=0; k<count; k++){
        a=nums[k]-mean;
        std=std+(a*a);
    }
    std/=(count);
    std=sqrt(std);
    fprintf(output,"Standard deviation: %f\r\n",std);
    fprintf(output,"\r\n");
   }

回答1:

A NaN can only have three origins in your code:

• mean is a NaN.
• In std/=(count); if count is 0.
• In std=sqrt(std); if std at this point is a negative number (seems impossible in your case).

You should debug your code and watch count and mean values (or print/export it) to find the why.

来源：https://stackoverflow.com/questions/29210975/1-qnan0-output-when-calculating-standard-deviation-c