如何preFIX（++ x）和后缀（X ++），操作的工作？ [英] How do Prefix (++x) and Postfix (x++) operations work?

问题描述

有人能告诉我如何preFIX /后缀运营商真的管用吗？我一直在寻找网上很多，但没有发现任何东西。

Can someone tell me how prefix / postfix operators really work? I've been looking online a lot but haven't found anything.

这是我可以告诉prefex先递增，然后进行操作，然后分配。结果
后缀会做第一次操作，然后分配，然后递增。

From what I can tell prefex first increments, then does the operation and then assigns.
Postfix would do the operation first, then assign and then increment.

但我有一点麻烦与我的code：

But I'm having a bit of trouble with my code:

int x, y;
x = 1;
y = x + x++; // (After operation y = 2)(x=2)

然而，当我做的：

However when I do:

y = x++ + x; // (After operation y = 3)(x=2)

我不知道为什么这些操作会有什么不同。我有两个问题：

I'm not sure why these operations would be any different. I have two questions:

• 您能解释的区别？

• Could you explain the difference?

这怎么也适用于其他运营商preFIX？

How does this apply to the other operator Prefix?

推荐答案

• 在C＃ + 的操作数左到右的顺序evaulated。


• 在C和C ++评价为 + 的操作数的顺序是unspecifed。

• In C# the operands of + are evaulated in left-to-right order.
• In C and C++ the order of evaluation for the operands of + is unspecifed.

对于C＃你的例子的工作方式如下：

For C# your examples work as follows:

 y = x + x++;
     ^ x is 1
         ^ x is increased to 2, but the postfix increment returns the old value (1)
 y = 2

 y = x++ + x;
     ^ x becomes 2, but postfix increment returns the old value (1)
           ^ x is now 2 here
 y = 3

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