Yyh Yyh - 1 month ago 5
C Question

I try to calculate a Standard deviation of less than 100 numbers in C

#include<stdio.h>
#include<math.h>
int main()
{
int n;
scanf("%d",&n);
int i=0,sum=0,average=0;
int num[100]={0};
double dvalue[100]={0.0};
double variance=0.0,s=0.0;
for(i=0;i<n;i++){//I just know this method to get the number array;
scanf("%d",&num[i]);
sum+=num[i];
}
average=sum/n;
for(i=0;i<n;i++){
dvalue[i]=num[i]-average;
dvalue[i]=pow(dvalue[i],2.0);//to get the (x-average)……2
variance+=dvalue[i];
}
s=sqrt(variance);
return 0;
}


this is my code,but it can't get the right answer.I am a new learner and this is the first time I seek help via stackoverflow I can't get the output why?
Thanks for every one .I actually debug at first ,but I can't know how to modify it ,sincerely thanks again

Answer

There were two things to correct:
1. type of average should be double
2. you have taken the variance incorrectly. after taking the sum of (x- average) you should divide it by n

#include<stdio.h>
#include<math.h>
int main()
{
    int n;
    scanf("%d", &n);
    int i = 0, sum = 0;
    double average = 0;
    int num[100] = { 0 };
    double dvalue[100] = { 0.0 };
    double variance = 0.0, s = 0.0;
    for (i = 0; i < n; i++) { //I just know this method to get the number array;
        scanf("%d", &num[i]);
        sum += num[i];
    }
    printf("sum %d\n", sum);
    average = sum;   
    average = average / n;
    printf("average %lf\n", average);
    for (i = 0; i < n; i++) {
        dvalue[i] = num[i] - average;
        dvalue[i] = pow(dvalue[i], 2.0); //to get the (x-average)……2
        variance += dvalue[i];
    }
    variance = variance / n; // population variance
    s = sqrt(variance);
    printf("varience %lf\n", variance);
    printf("Population Standard deviation %lf", s);

    return 0;
}

edited the answer according to @chux advice

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