blocks|key|3246117|text|如果我想将一个变量设置为请求中发送的值(如果它是已定义的)，或者设置为某个默认值(如果它没有定义)，我发现在进行web开发时特别有用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3246118|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I find it particularly helpful when doing web development if I want to set a variable to a value sent in the request if it is defined or to some default value if it is not.

blocks|key|3032158|text|我基本上推荐仅当结果语句非常简短，并且在不牺牲可读性的情况下比if/else等效语句的简洁性有了显着提高时才使用它。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3032159|一个很好的例子：|3032160|int+result+=+Check()+?+1+:+0;|code-block|syntax|javascript|3032161|糟糕的例子：|3032162|int+result+=+FirstCheck()+?+1+:+SecondCheck()+?+1+:+ThirdCheck()+?+1+:+0;|3032163|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I would basically recommend using it only when the resulting statement is extremely short and represents a significant increase in conciseness over the if/else equivalent without sacrificing readability.

Good example:

<pre><code>int result = Check() ? 1 : 0;
</code></pre>

Bad example:

<pre><code>int result = FirstCheck() ? 1 : SecondCheck() ? 1 : ThirdCheck() ? 1 : 0;
</code></pre>

blocks|key|302591|text|如果我要设置一个值，并且我知道它总是需要一行代码来完成，我通常会使用三元(条件)运算符。如果我的代码和逻辑将来可能会改变，我会使用if/else，因为这对其他程序员来说更清楚。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|302592|您更感兴趣的可能是??+operator。|offset|length|302593|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-US/library/ms173224%2528v=VS.80%2529.aspx^0|0|9|B|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

If I'm setting a value and I know it will always be one line of code to do so, I typically use the ternary (conditional) operator. If there's a chance my code and logic will change in the future, I use an if/else as it's more clear to other programmers. 

Of further interest to you may be the <a href="http://msdn.microsoft.com/en-US/library/ms173224%28v=VS.80%29.aspx" rel="nofollow noreferrer">?? operator</a>.

blocks|key|301872|text|条件运算符的优点是它是一个运算符。换句话说，它返回一个值。因为if是一条语句，所以它不能返回值。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|301873|entityMap^0|V|2|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

The advantage of the conditional operator is that it is an operator. In other words, it returns a value. Since <code>if</code> is a statement, it cannot return a value.

blocks|key|3032216|text|在使用三元运算符时需要认识到的一件事是，它是一个表达式，而不是一个语句。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3032217|在像scheme这样的函数式语言中，这种区别是不存在的：|3032218|(如果(>+a+b)+a+b)|3032219|条件?：运算符“看起来没有if/else构造那么灵活”|3032220|在函数式语言中是这样的。|3032221|当使用命令式语言编程时，我会在通常使用表达式(赋值、条件语句等)的情况下应用三元运算符。|3032222|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|P|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|Q|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|R|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|S|8|@]|9|@]|A|$]]|$1|L|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|M|$]]

One thing to recognize when using the ternary operator that it is an expression not a statement. 

In functional languages like scheme the distinction doesn't exists:

(if (> a b) a b)

Conditional ?: Operator
"Doesn't seem to be as flexible as the if/else construct"

In functional languages it is.

When programming in imperative languages I apply the ternary operator in situations where I typically would use expressions (assignment, conditional statements, etc).

blocks|key|3246310|text|我建议将三元(？：)运算符的使用限制为简单的单行if/else逻辑赋值。类似于这个图案的东西：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3246311|if(<boolCondition>)+{
++++<variable>+=+<value>;
}
else+{
++++<variable>+=+<anotherValue>;
}|code-block|syntax|javascript|3246312|可以很容易地转换为：|3246313|<variable>+=+<boolCondition>+?+<value>+:+<anotherValue>;|3246314|我会避免在需要if/else+if/else、嵌套if/else或if/else分支逻辑导致多行求值的情况下使用三元运算符。在这些情况下应用三元运算符可能会导致不可读、令人困惑和无法管理的代码。希望这能有所帮助。|3246315|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

I'd recommend limiting the use of the ternary(?:) operator to simple single line assignment if/else logic. Something resembling this pattern:

<pre><code>if(&lt;boolCondition&gt;) {
 &lt;variable&gt; = &lt;value&gt;;
}
else {
 &lt;variable&gt; = &lt;anotherValue&gt;;
}
</code></pre>

Could be easily converted to:

<pre><code>&lt;variable&gt; = &lt;boolCondition&gt; ? &lt;value&gt; : &lt;anotherValue&gt;;
</code></pre>

I would avoid using the ternary operator in situations that require if/else if/else, nested if/else, or if/else branch logic that results in the evaluation of multiple lines. Applying the ternary operator in these situations would likely result in unreadable, confusing, and unmanageable code. Hope this helps.

blocks|key|3032417|text|条件运算符非常适用于短条件，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3032418|varA+=+boolB+?+valC+:+valD;|code-block|syntax|javascript|3032419|我偶尔会使用它，因为这样写东西花的时间更少……不幸的是，在浏览您的代码时，其他开发人员有时可能会忽略此分支。另外，代码通常不会那么短，所以我通常通过将？和:在单独的行上，如下所示：|3032420|doSomeStuffToSomething(shouldSomethingBeDone()
++++?+getTheThingThatNeedsStuffDone()
++++:+getTheOtherThingThatNeedsStuffDone());|3032421|然而，使用if/else块的最大优势(这也是我更喜欢它们的原因)是，它更容易在以后加入并向分支添加一些额外的逻辑，|3032422|if+(shouldSomethingBeDone())+{
++++doSomeStuffToSomething(getTheThingThatNeedsStuffDone());
++++doSomeAdditionalStuff();
}+else+{
doSomeStuffToSomething(getTheOtherThingThatNeedsStuffDone());
}|3032423|或者添加另一个条件：|3032424|if+(shouldSomethingBeDone())+{
++++doSomeStuffToSomething(getTheThingThatNeedsStuffDone());
++++doSomeAdditionalStuff();
}+else+if+(shouldThisOtherThingBeDone()){
++++doSomeStuffToSomething(getTheOtherThingThatNeedsStuffDone());
}|3032425|所以，最后，这是关于您的便利性的(简写为:?)对您(和其他人)的便利。这是一个判断的决定。但像所有其他代码格式问题一样，唯一的真正规则是保持一致，并在视觉上礼貌地对待那些必须维护(或评分！)的人。你的代码。|3032426|(所有代码都是眼睛编译的)|3032427|entityMap^0|0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|10|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|14|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|15|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|16|8|@]|9|@]|A|$]]|$1|U|3|V|5|6|7|17|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|18|8|@]|9|@]|A|$]]]|X|$]]

The conditional operator is great for short conditions, like this:

<pre><code>varA = boolB ? valC : valD;
</code></pre>

I use it occasionally because it takes less time to write something that way... unfortunately, this branching can sometimes be missed by another developer browsing over your code. Plus, code isn't usually that short, so I usually help readability by putting the ? and : on separate lines, like this:

<pre><code>doSomeStuffToSomething(shouldSomethingBeDone()
 ? getTheThingThatNeedsStuffDone()
 : getTheOtherThingThatNeedsStuffDone());
</code></pre>

However, the big advantage to using if/else blocks (and why I prefer them) is that it's easier to come in later and add some additional logic to the branch,

<pre><code>if (shouldSomethingBeDone()) {
 doSomeStuffToSomething(getTheThingThatNeedsStuffDone());
 doSomeAdditionalStuff();
} else {
doSomeStuffToSomething(getTheOtherThingThatNeedsStuffDone());
}
</code></pre>

or add another condition:

<pre><code>if (shouldSomethingBeDone()) {
 doSomeStuffToSomething(getTheThingThatNeedsStuffDone());
 doSomeAdditionalStuff();
} else if (shouldThisOtherThingBeDone()){
 doSomeStuffToSomething(getTheOtherThingThatNeedsStuffDone());
}
</code></pre>

So, in the end, it's about convenience for you now (shorter to use :?) vs. convenience for you (and others) later. It's a judgment call... but like all other code-formatting issues, the only real rule is to be consistent, and be visually courteous to those who have to maintain (or grade!) your code.

(all code eye-compiled)

blocks|key|302679|text|使用？运算符。MS+Visual+C%2B%2B，但这实际上是一个编译器特定的事情。在某些情况下，编译器实际上可以优化出条件分支。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|302680|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

There is some performance benefit of using the the ? operator in eg. MS Visual C++, but this is a really a compiler specific thing. The compiler can actually optimize out the conditional branch in some cases.

blocks|key|3246478|text|我发现自己最常使用的场景是默认值，尤其是在返回时|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3246479|return+someIndex+<+maxIndex+?+someIndex+:+maxIndex;|code-block|syntax|javascript|3246480|我真的觉得只有这些地方很好，但对他们来说，我觉得很好。|3246481|但是，如果您正在寻找布尔值，这有时看起来可能是一件合适的事情：|3246482|bool+hey+=+whatever+<+whatever_else+?+true+:+false;|3246483|因为它很容易阅读和理解，但这个想法应该总是被抛到更明显的地方：|3246484|bool+hey+=+(whatever+<+whatever_else);|3246485|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

The scenario I most find myself using it is for defaulting values and especially in returns

<pre><code>return someIndex &lt; maxIndex ? someIndex : maxIndex;
</code></pre>

Those are really the only places I find it nice, but for them I do.

Though if you're looking for a boolean this might sometimes look like an appropriate thing to do:

<pre><code>bool hey = whatever &lt; whatever_else ? true : false;
</code></pre>

Because it's so easy to read and understand, but that idea should always be tossed for the more obvious:

<pre><code>bool hey = (whatever &lt; whatever_else);
</code></pre>

blocks|key|3246498|text|如果在同一条件下需要多个分支，请使用if：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3246499|if+(A+==+6)
++f(1,+2,+3);
else
++f(4,+5,+6);|code-block|syntax|javascript|3246500|如果您需要具有不同条件的多个分支，那么如果语句计数会滚雪球，那么您将需要使用三元：|3246501|f(+(A+==+6)?+1:+4,+(B+==+6)?+2:+5,+(C+==+6)?+3:+6+);|3246502|此外，您还可以在初始化时使用三元运算符。|3246503|const+int+i+=+(A+==+6)?+1+:+4;|3246504|用if来做这件事是非常混乱的：|3246505|int+i_temp;
if+(A+==+6)
+++i_temp+=+1;
else
+++i_temp+=+4;
const+int+i+=+i_temp;|3246506|您不能将初始化放在if/else中，因为它会更改作用域。但是引用和常量变量只能在初始化时绑定。|3246507|entityMap^0|0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|X|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Y|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|10|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|11|8|@]|9|@]|A|$E|F]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$]]|$1|Q|3|R|5|D|7|13|8|@]|9|@]|A|$E|F]]|$1|S|3|T|5|6|7|14|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|15|8|@]|9|@]|A|$]]]|V|$]]

If you need multiple branches on the same condition, use an if:

<pre><code>if (A == 6)
 f(1, 2, 3);
else
 f(4, 5, 6);
</code></pre>

If you need multiple branches with different conditions, then if statement count would snowball, you'll want to use the ternary:

<pre><code>f( (A == 6)? 1: 4, (B == 6)? 2: 5, (C == 6)? 3: 6 );
</code></pre>

Also, you can use the ternary operator in initialization.

<pre><code>const int i = (A == 6)? 1 : 4;
</code></pre>

Doing that with if is very messy:

<pre><code>int i_temp;
if (A == 6)
 i_temp = 1;
else
 i_temp = 4;
const int i = i_temp;
</code></pre>

You can't put the initialization inside the if/else, because it changes the scope. But references and const variables can only be bound at initialization.

blocks|key|3032568|text|我通常会选择一个三元运算符，否则我会有很多重复的代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3032569|if+(a+>+0)
++++answer+=+compute(a,+b,+c,+d,+e);
else
++++answer+=+compute(-a,+b,+c,+d,+e);|code-block|syntax|javascript|3032570|对于三元运算符，这可以通过以下操作来完成。|3032571|answer+=+compute(a+>+0+?+a+:+-a,+b,+c,+d,+e);+|3032572|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

I usually choose a ternary operator when I'd have a lot of duplicate code otherwise.

<pre><code>if (a &gt; 0)
 answer = compute(a, b, c, d, e);
else
 answer = compute(-a, b, c, d, e);
</code></pre>

With a ternary operator, this could be accomplished with the following.

<pre><code>answer = compute(a &gt; 0 ? a : -a, b, c, d, e); 
</code></pre>

blocks|key|304849|text|三元运算符可以包含在rvalue中，而if-then-else不能；另一方面，if-then-else可以执行循环和其他语句，而三元运算符只能执行(可能无效)rvalue。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|304850|需要注意的是，&&和%7C%7C运算符允许使用if-then-else实现一些更难实现的执行模式。例如，如果有几个函数要调用，并且希望在其中任何一个失败时执行一段代码，那么可以使用&&运算符很好地完成这一任务。如果不使用该运算符，将需要冗余代码、goto或额外的标志变量。|304851|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

The ternary operator can be included within an rvalue, whereas an if-then-else cannot; on the other hand, an if-then-else can execute loops and other statements, whereas the ternary operator can only execute (possibly void) rvalues.

On a related note, the &amp;&amp; and || operators allow some execution patterns which are harder to implement with if-then-else. For example, if one has several functions to call and wishes to execute a piece of code if any of them fail, it can be done nicely using the &amp;&amp; operator. Doing it without that operator will either require redundant code, a goto, or an extra flag variable.

blocks|key|299812|text|其他答案几乎涵盖了这一点，但“这是一个表达式”并不能真正解释为什么它如此有用……|type|unstyled|depth|inlineStyleRanges|entityRanges|data|299813|在C%2B%2B和C#等语言中，您可以使用它们定义局部只读字段(在方法体中)。这对于传统的if/then语句是不可能的，因为只读字段的值必须在单个语句中赋值：|299814|readonly+int+speed+=+(shiftKeyDown)+?+10+:+1;|code-block|syntax|javascript|299815|与以下内容不同：|299816|readonly+int+speed;++
if+(shifKeyDown)++
++++speed+=+10;++++//+error+-+can't+assign+to+a+readonly
else++
++++speed+=+1;+++++//+error++|299817|以类似的方式，您可以在其他代码中嵌入第三级表达式。除了使源代码更紧凑(在某些情况下更具可读性)，它还可以使生成的机器码更紧凑、更高效：|299818|MoveCar((shiftKeyDown)+?+10+:+1);|299819|与两次调用同一个方法相比，...may生成的代码更少：|299820|if+(shiftKeyDown)
++++MoveCar(10);
else
++++MoveCar(1);|299821|当然，它也是一种更方便、更简洁的形式(键入更少，重复更少，如果必须在if+/else中复制代码块，还可以减少出错的机会)。在干净的“公共模式”案例中，如下所示：|299822|object+thing+=+(reference+==+null)+?+null+:+reference.Thing;|299823|..。它的阅读/解析/理解(一旦你习惯了)比冗长的if/else等价物更快，所以它可以帮助你更快地“摸索”代码。|299824|当然，仅仅因为它有用并不意味着它在所有情况下都是最好的。我建议只在意义明确(或更清楚)的小段代码中使用?:+-如果你在更复杂的代码中使用它，或者在彼此之间嵌套三元运算符，它可能会使代码非常难以阅读。|offset|length|style|CODE|299825|entityMap^0|0|0|0|0|0|0|0|0|0|0|0|0|1F|2|0^^$0|@$1|2|3|4|5|6|7|18|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|19|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1A|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1B|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1C|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|1D|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|1E|8|@]|9|@]|A|$G|H]]|$1|Q|3|R|5|6|7|1F|8|@]|9|@]|A|$]]|$1|S|3|T|5|F|7|1G|8|@]|9|@]|A|$G|H]]|$1|U|3|V|5|6|7|1H|8|@]|9|@]|A|$]]|$1|W|3|X|5|F|7|1I|8|@]|9|@]|A|$G|H]]|$1|Y|3|Z|5|6|7|1J|8|@]|9|@]|A|$]]|$1|10|3|11|5|6|7|1K|8|@$12|1L|13|1M|14|15]]|9|@]|A|$]]|$1|16|3|-4|5|6|7|1N|8|@]|9|@]|A|$]]]|17|$]]

This is pretty much covered by the other answers, but "it's an expression" doesn't really explain why that is so useful...

In languages like C++ and C#, you can define local readonly fields (within a method body) using them. This is not possible with a conventional if/then statement because the value of a readonly field has to be assigned within that single statement:

<pre><code>readonly int speed = (shiftKeyDown) ? 10 : 1;
</code></pre>

is not the same as:

<pre><code>readonly int speed; 
if (shifKeyDown) 
 speed = 10; // error - can't assign to a readonly
else 
 speed = 1; // error 
</code></pre>

In a similar way you can embed a tertiary expression in other code. As well as making the source code more compact (and in some cases more readable as a result) it can also make the generated machine code more compact and efficient:

<pre><code>MoveCar((shiftKeyDown) ? 10 : 1);
</code></pre>

...may generate less code than having to call the same method twice:

<pre><code>if (shiftKeyDown)
 MoveCar(10);
else
 MoveCar(1);
</code></pre>

Of course, it's also a more convenient and concise form (less typing, less repetition, and can reduce the chance of errors if you have to duplicate chunks of code in an if/else). In clean "common pattern" cases like this:

<pre><code>object thing = (reference == null) ? null : reference.Thing;
</code></pre>

... it is simply faster to read/parse/understand (once you're used to it) than the long-winded if/else equivalent, so it can help you to 'grok' code faster.

Of course, just because it is useful does not mean it is the best thing to use in every case. I'd advise only using it for short bits of code where the meaning is clear (or made more clear) by using <code>?:</code> - if you use it in more complex code, or nest ternary operators within each other it can make code horribly difficult to read.

blocks|key|3032725|text|一个非常酷的用法是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3032726|x+=+foo+?+1+:
++++bar+?+2+:
++++baz+?+3+:
++++++++++4;|code-block|syntax|javascript|3032727|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

A really cool usage is:

<pre><code>x = foo ? 1 :
 bar ? 2 :
 baz ? 3 :
 4;
</code></pre>

blocks|key|3246786|text|虽然上面的答案是有效的，我也同意可读性很重要，但还有两点需要考虑：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3246787|3246788|在C#6中，您可以使用表达式体方法。|ordered-list-item|3246789|3246790|这使得三元组的使用特别简洁：|3246791|string+GetDrink(DayOfWeek+day)+
+++=>+day+==+DayOfWeek.Friday
++++++?+"Beer"+:+"Tea";|code-block|syntax|javascript|3246792|当涉及到隐式类型转换时，|3246793|的行为有所不同。|3246794|3246795|如果您的T1和T2类型都可以隐式转换为T，则下面的不能用于：|offset|length|style|CODE|BOLD|3246796|T+GetT()+=>+true+?+new+T1()+:+new+T2();|3246797|(因为编译器尝试确定三元表达式的类型，并且T1和T2之间不存在转换。)|3246798|另一方面，下面的if/else版本可以工作：|3246799|T+GetT()
{
+++if+(true)+return+new+T1();
+++return+new+T2();
}|3246800|因为T1被转换为T，T2也是如此|3246801|entityMap^0|0|0|0|0|0|0|0|0|0|4|2|7|2|J|1|P|4|0|0|L|2|O|2|0|8|7|0|0|2|2|8|1|A|2|0^^$0|@$1|2|3|4|5|6|7|1B|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|1C|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|1D|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|1E|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|1F|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|1G|8|@]|9|@]|A|$L|M]]|$1|N|3|O|5|6|7|1H|8|@]|9|@]|A|$]]|$1|P|3|Q|5|E|7|1I|8|@]|9|@]|A|$]]|$1|R|3|-4|5|6|7|1J|8|@]|9|@]|A|$]]|$1|S|3|T|5|6|7|1K|8|@$U|1L|V|1M|W|X]|$U|1N|V|1O|W|X]|$U|1P|V|1Q|W|X]|$U|1R|V|1S|W|Y]]|9|@]|A|$]]|$1|Z|3|10|5|K|7|1T|8|@]|9|@]|A|$L|M]]|$1|11|3|12|5|6|7|1U|8|@$U|1V|V|1W|W|X]|$U|1X|V|1Y|W|X]]|9|@]|A|$]]|$1|13|3|14|5|6|7|1Z|8|@$U|20|V|21|W|X]]|9|@]|A|$]]|$1|15|3|16|5|K|7|22|8|@]|9|@]|A|$L|M]]|$1|17|3|18|5|6|7|23|8|@$U|24|V|25|W|X]|$U|26|V|27|W|X]|$U|28|V|29|W|X]]|9|@]|A|$]]|$1|19|3|-4|5|6|7|2A|8|@]|9|@]|A|$]]]|1A|$]]

While the above answers are valid, and I agree with readability being important, there are 2 further points to consider:

<ol>
<li>In C#6, you can have expression-bodied methods. </li>
</ol>

This makes it particularly concise to use the ternary:

<pre><code>string GetDrink(DayOfWeek day) 
 =&gt; day == DayOfWeek.Friday
 ? "Beer" : "Tea";
</code></pre>

<ol start="2">
<li>Behaviour differs when it comes to implicit type conversion.</li>
</ol>

If you have types <code>T1</code> and <code>T2</code> that can both be implicitly converted to <code>T</code>, then the below does not work:

<pre><code>T GetT() =&gt; true ? new T1() : new T2();
</code></pre>

(because the compiler tries to determine the type of the ternary expression, and there is no conversion between <code>T1</code> and <code>T2</code>.)

On the other hand, the <code>if/else</code> version below does work:

<pre><code>T GetT()
{
 if (true) return new T1();
 return new T2();
}
</code></pre>

because <code>T1</code> is converted to <code>T</code> and so is <code>T2</code>

blocks|key|3246808|text|有时，它可以使布尔值的赋值在第一眼看起来更容易阅读：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3246809|//+With
button.IsEnabled+=+someControl.HasError+?+false+:+true;

//+Without
button.IsEnabled+=+!someControl.HasError;|code-block|syntax|javascript|3246810|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Sometimes it can make the assignment of a bool value easier to read at first glance:

<pre><code>// With
button.IsEnabled = someControl.HasError ? false : true;

// Without
button.IsEnabled = !someControl.HasError;
</code></pre>

blocks|key|3246872|text|使用C#+7，您可以使用新的功能来简化ref兼容变量的条件赋值。所以现在，你不仅可以做到：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|3246873|int+i+=+0;

T+b+=+default(T),+c+=+default(T);

//+initialization+of+C#7+'ref-local'+variable+using+a+conditional+r-value⁽¹⁾

ref+T+a+=+ref+(i+==+0+?+ref+b+:+ref+c);|code-block|syntax|javascript|3246874|...but也是非常棒的：|3246875|//+assignment+of+l-value⁽²⁾+conditioned+by+C#7+'ref-locals'

(i+==+0+?+ref+b+:+ref+c)+=+a;|3246876|该行代码将a的值赋给b或c，具体取决于i的值。|CODE|3246877|3246878|笔记|3246879|3246880|是赋值的右边，即被赋值的值。|ordered-list-item|3246881|3246882|3246883|是赋值的左边，也就是接收赋值的变量。|3246884|3246885|​|3246886|entityMap^0|2|4|0|0|0|0|5|1|A|1|C|1|J|1|0|0|0|2|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|17|8|@$9|18|A|19|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|1B|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|1C|8|@]|D|@]|E|$I|J]]|$1|O|3|P|5|6|7|1D|8|@$9|1E|A|1F|B|Q]|$9|1G|A|1H|B|Q]|$9|1I|A|1J|B|Q]|$9|1K|A|1L|B|Q]]|D|@]|E|$]]|$1|R|3|-4|5|6|7|1M|8|@]|D|@]|E|$]]|$1|S|3|T|5|6|7|1N|8|@$9|1O|A|1P|B|C]]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1Q|8|@]|D|@]|E|$]]|$1|V|3|W|5|X|7|1R|8|@]|D|@]|E|$]]|$1|Y|3|-4|5|6|7|1S|8|@]|D|@]|E|$]]|$1|Z|3|-4|5|6|7|1T|8|@]|D|@]|E|$]]|$1|10|3|11|5|X|7|1U|8|@]|D|@]|E|$]]|$1|12|3|-4|5|6|7|1V|8|@]|D|@]|E|$]]|$1|13|3|14|5|6|7|1W|8|@]|D|@]|E|$]]|$1|15|3|-4|5|6|7|1X|8|@]|D|@]|E|$]]]|16|$]]

With C# 7, you can use the new <a href="https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/classes-and-structs/ref-returns" rel="nofollow noreferrer">ref locals</a> feature to simplify the conditional assignment of ref-compatible variables. So now, not only can you do:

<pre><code>int i = 0;

T b = default(T), c = default(T);

// initialization of C#7 'ref-local' variable using a conditional r-value⁽¹⁾

ref T a = ref (i == 0 ? ref b : ref c);
</code></pre>

...but also the extremely wonderful:

<pre><code>// assignment of l-value⁽²⁾ conditioned by C#7 'ref-locals'

(i == 0 ? ref b : ref c) = a;
</code></pre>

That line of code assigns the value of <code>a</code> to either <code>b</code> or <code>c</code>, depending on the value of <code>i</code>.

 
<hr>
Notes 
1. <a href="https://en.wikipedia.org/wiki/Value_(computer_science)" rel="nofollow noreferrer">r-value</a> is the right-hand side of an assignment, the value that gets assigned. 
2. <a href="https://en.wikipedia.org/wiki/Value_(computer_science)" rel="nofollow noreferrer">l-value</a> is the left-hand side of an assignment, the variable that receives the assigned value.

What are the benefits and drawbacks of the ?: operator as opposed to the standard if-else statement. The obvious ones being:

Conditional ?: Operator

<ul>
<li>Shorter and more concise when dealing with direct value comparisons and assignments</li>
<li>Doesn't seem to be as flexible as the if/else construct</li>
</ul>

Standard If/Else

<ul>
<li>Can be applied to more situations (such as function calls) </li>
<li>Often are unnecessarily long</li>
</ul>

Readability seems to vary for each depending on the statement. For a little while after first being exposed to the ?: operator, it took me some time to digest exactly how it worked. Would you recommend using it wherever possible, or sticking to if/else given that I work with many non-programmers?

Benefits of using the conditional ?: (ternary) operator

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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相对于标准的if-else语句，?：运算符的优点和缺点是什么。最明显的是：Conditional ?：Operator在处理直接值比较和assignmentsDoesn't时，更简短、更简洁，其灵活性似乎与if/else 一样标准If/Else可以应用于更多的情况(例如函数调用)通常不必要地很长根据语句的不同，可读性似...

问使用条件?：(三元)运算符的好处
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