c++问题，随机数，平均值，标准差，数组

. 随机产生100个位于【-100，100】之间的整数并保存在数组里，统计数组中的正数、负数的个数，计算平均值和标准差。

#include<iostream>
#include<cstdlib>
#include<ctime>
#include<cmath>
using namespace std;
int a[100];
int main() {
    srand(time(0));
    for(int i = 0; i < 100; i++) {
        a[i] = rand() % 201 - 100;
    }
    double s = 0, s2 = 0, ave, sn;
    int n = 0, m = 0;
    for(int i = 0; i < 100; i++) {
        if(a[i] > 0) n++;
        else if(a[i] < 0) m++;
        s += a[i];
    }
    ave = s / 100;
    for(int i = 0; i < 100; i++) {
        s2 = s2 + pow(a[i] - ave, 2);
    }
    sn = sqrt(s2 / 100);
    cout << "正数个数：" << n << endl;
    cout << "负数个数：" << m << endl;
    cout << "平均值：" << ave << endl;
    cout << "标准差：" << sn << endl;
    return 0;
}