急于操作和短路操作之间的差异？ （| versu ||和与放大器; versu和放大器;＆安培;） [英] Difference between eager operation and short-circuit operation? (| versu || and & versu &&)

问题描述

我（仍然）学习C＃ - 我想我明白和放大器之间的区别; ＆放大器; ＆功放;＆安培; 以及 | ＆放大器; || ...

I am (still) learning C# - and I thought I understood the difference between & & && as well as | & ||...

不过，只是读另一位导游后，很显然我不明白这一点。

However, after just reading another guide, it is clear I don't get it.

我写了一个小真值表正如我认为，他们返回相同的。从我已阅读，采用双层符号听起来像是一个出色的解决方案，但我上的区别有点迷茫，不知道是否有人能解释一下/给出为什么/时，你会使用一个，而不是其他的例子 - 我试着阅读MSDN的例子，但它留给我比当我开始更糊涂！

I wrote a little truth table and as I thought, they return the same. From what I have read, using double symbols sounds like a superior solution, but I am a little confused on the difference and was wondering if anyone could please explain/give an example why/when you would use one instead of the other - I tried reading the MSDN example, but it left me more confused than when I started!

（而且，如果有人能拿出一个更好的标题，随意改变它...非常尴尬写一个！）

(And, if anyone can come up with a better title, feel free to change it... very awkward to write one!)

推荐答案

＆放大器;可以使用两种不同的方法：按位和和逻辑与

& can be used in two different ways: bitwise "and" and logical "and"

逻辑安培之间的差额;并与功放;＆安培;是仅在情况下，你使用＆安培;中，第二前pression进行了评价，即使第一前pression已经假。如果你想在循环初始化两个变量，这可能（例如）是有趣的：

The difference between logical & and && is only that in case you use &, the second expression is also evaluated, even if the first expression was already false. This may (for example) be interesting if you want to initialize two variables in the loop:

if ((first = (i == 7)) & (second = (j == 10))) { //do something }

如果您使用此语法，第一和第二总会有一个值，如果你使用

if you use this syntax, first and second will always have a value, if you use

if ((first = (i == 7)) && (second = (j == 10))) { //do something }

它可以是只具有第一后的评价值。

it may be that only first has a value after the evaluation.

有相同|和||：在您使用的情况下，|，无论是前pressions的一直被运用，如果你用||它可以是只在第一个前pression被计算，这将是该情况下，如果第一前pression为真

It is the same for | and ||: In case you use |, both of the expressions are always evaluated, if you use || it may be that only the first expression is evaluated, which would be the case if the first expression is true.

在另一方面，在其它应用＆安培;＆安培;可能是更好的选择。如果为mynumber的类型是诠释？中，你可以有像

In contrast, in other applications && can be the better choice. If myNumber is of type int?, you could have something like

if (myNumber != null && myNumber.Value == 7)

和这只能评估为mynumber！= NULL 首先，它只会计算第二个前pression，如果空检查是好的。

and this would only evaluate myNumber != null at first, and it would only evaluate the second expression, if the null check was okay.

if (myNumber != null & myNumber.Value == 7)

将与一个NullPointerException异常的第二个前pression在评估过程中完成，如果为mynumber为空。因此，你可以使用和放大器;＆安培;在这方面

would finish with a NullPointerException during the evaluation of the second expression, if myNumber was null. Therefore, you would use && in this context.

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