java - java中对前N个数字求和

Question

Hello, I am new to programming and I am trying to write a small program where it will calculate the sum for first N numbers. The problem is it does not work for even numbers. I have not managed to figure out why. My code is as follow:

int n = Integer.parseInt(args[0]);
    int sum = (1+n)/2*n;
    System.out.println(sum + " is the sum of first " + n + " numbers");

Answer 1

它甚至不适用于 n，因为 (n+1)/2 被截断为 int。

这意味着，例如，如果 n=4，(n+1)/2 结果为 2 而不是 2.5，因此当您将其乘以 n 时，您得到 8，而不是所需的 10。

您只需更改操作顺序即可解决此问题。如果您首先将 n 乘以 (n+1)，则结果保证是偶数，因此将其除以 2 将得出正确的答案。

int sum = n*(1+n)/2;