为什么我一直在c ++中输出错误的输出

Question

int main()
{
int n, i, sum;

cout << "Enter a value for n: ";
cin >> n;
sum = 0;

    i = 1;
    do
{
    sum += i * i;
    i++;
}while (i <= n);
cout << "The sum of the first " << n
    << " numbers is " << sum << endl;

return 0;
}

每当我运行此代码并使用4作为示例时，输出变为30.当4的阶乘为24时

Answer 1

sum+=i*i 

- ＆GT;第一个n方格的总和。

factorial是

prod=prod*i