计算1-n的奇数和

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    while(cin>>n)
    {

        int sum = 0;
        for(int i = 1; i <= n; i++)
        {
            sum += (i%2 == 0? 0:i);
        }
        cout<<"sum "<<sum<<endl;
        int ans = (n%2 == 0) ? (((n)/2)*(1+n-1)/2) : (((n+1)/2)*(1+n)/2);
        cout<<"ans: "<<ans<<endl;
        cout<<"_____________"<<endl;
    }
    return 0;
}