summation of alternating function in c++

If the input is 4 the output should be 2—>
f(4) =  - 1  + 2  - 3  + 4  = 2

but the code doesn’t give any output

#include <iostream>
using namespace std;

int main() {
    int n; cin>>n;
    int sum = 0;
    for(int i = 1;i<=n;i++){
        if (i%2 != 0){
            i = -i;
        }
        sum += i;
    }
    cout<<sum;
    return 0;
}

>Solution :

You need an endl when printing so that the output buffer gets flushed to the console.

cout << sum << endl;

e:
In the for loop, you set i = -i. This makes it so that i will never be able to reach n.

for (int i = 1; i <=n; i++) {
    if (i%2 == 0)
        sum += i;
    else
        sum -= i;
}