求方差

#include <stdio.h>   
double fangcha(int *arr,int n)  
{  
    int i;  
    double sum1=0,sum2=0;  
    for(i=0;i<n;i++)  
    {  
        sum1+=arr[i]*arr[i];  
        sum2+=arr[i];  
    }  
    return sum1/n-(sum2/n)*(sum2/n);  
}  
int main()  
{  
    int arr[3]={1,2,3};  
    printf("%f\n",fangcha(arr,3));  
    return 0;  
}