下面程序可以正确计算并输出3名学生的平均成绩。

struct Student {
    int id;
    int score;
};
int main() {
    Student students[3] = {
        {1, 90},
        {2, 80},
        {3, 100}
    };
    int sum = 0;
    for (int i = 0; i < 3; i++) {
        sum += students[i].score;
    }
    double average = sum / 3.0;
    cout << average << endl;
    return 0;
}