英文:
Trying to understand --x vs x-- in C++
问题
我正在尝试评估这个问题，尽管它很简单，但我似乎无法理解。我得到的答案是16，但提供的答案是12。我不明白这怎么可能是12。
我首先执行了--x，所以y的值应该是4，然后我需要与x--相乘，但由于它是在之后评估的，所以它的值也是4，然后x被递减为3。所以4*4=16。
有人能解释一下我的推理有什么问题吗？
int x, y;
x = 5;
y = --x * x--;
std::cout << y;
英文:
I am trying to evaluate this, and even if is is quite simple, I can't seem to understand it. I got 16, but the provided answer was 12. I don't understand how this can be 12.
I did --x first, so first y would be 4, then I need to multiply with x--, but it will be 4 too since it is evaluated after, and the x being decremented after that to 3. So 4*4 = 16.
Can someone explain what is wrong in my reasoning?
int x, y;
x = 5;
y = --x * x--;
std::cout << y;
答案1
得分: 5
你不能确定--x和x--哪个先被计算，所以结果是未定义的。
英文:
You are not guaranteed whether --x or x-- is evaluated first, so the result is undefined.
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