在 Cpp 中，从 function 无法正常工作

Question

I need to do this exercise, with struct and include the function in the struct to do the calculations, but for some reason, it's not working. I recommended you to check the image for a better idea.

#include <iostream>
using namespace std;
struct Alfa{
    double h,x,n,a;
    void shuma(){
        cout << "enter n: "; cin >> n;
        cout << "enter a: "; cin >> a;
        for (int i = 1; i >= n; i++){
            x = 2 * i + a;
        }
    };
};

int main() {
    Alfa alf;
    alf.shuma();
        alf.h = (alf.x / 2) + 3;

    cout <<  alf.h;

    return 0;
}

Answer 1

You are not following the formula in the image. Use this instead:

double sum = 0;
for (int i = 1; i <= n + 1; i++) {
    if (i != 4) {
        sum += 2 * i + a;
    }
}
h = x / 2 + 3 * sum;

Answer 2

for (int i = 1; i >= n; i++) means i initiated to 1, while i>=n do the loop, then inc i . So when n is bigger then 1, it will never enter the loop. Maybe you want for (int i = 1; i <= n+1; i++) ?