#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 ",fangcha(arr,3)); return 0; }