Help with the implementation of the task

Godmode_Abuser, ( cos x + cos 2x + ... + (-1) ^ (n+1) * cos nx... )
Как я понимаю формула правильная нужна:

Вот код:

#include <iostream>
#include <cmath>
int main()
{
double x;
std::cout << "x = "; std::cin >> x;
int n;
std::cout << "n = "; std::cin >> n;
int sign = 1;
double s = 0.0;
for (int i = 1; i <= n; i++)
{
s += sign * cos(i * x);
sign = -sign;
}
std::cout << "s = " << s;
return 0;
}

C

#include <iostream>

#include <cmath>

int main()

{

    double x;

    std::cout << "x = "; std::cin >> x;

    int n;

    std::cout << "n = "; std::cin >> n;

    int sign = 1;

    double s = 0.0;

    for (int i = 1; i <= n; i++)

    {

        s += sign * cos(i * x);

        sign = -sign;

    }

    std::cout << "s = " << s;

    return 0;

}