循环结构

for循环简单顺序求和

#include <iostream>
using namespace std;
int main()
{
    int n,i,sum=0;
    cin >> n;
    for(i=1;i<=n;i++)//1+2+3+4+...+n
    {
        sum = sum+i;
    }
    cout << sum << endl;
    return 0;
}

for循环任意数求和

#include <iostream>
#include<iomanip>
using namespace std;
int main()
{
    int n;
    double num, sum = 0, aver = 0;
    cin >> n;
    for (int i = 1; i <= n; i++)
    {
        cin >> num;
        sum += num;
    }
    aver = sum / n;
    cout << sum << " " << fixed << setprecision(5) << aver << endl;
}