blocks|key|1375428|text|它们有不同的含义。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1375429|第一个示例将在满足条件时停止。|1375430|第二个将测试$x两次。|offset|length|style|CODE|1375431|你可能想让你的第二个if成为else+if。这意味着一旦一个条件的计算结果为真，该块就会被跳过。|1375432|但如果你想知道哪一个是最快的，你应该考虑哪一个最有效地传达了我想要做的事情。它们很可能都会在目标架构中以条件跳转的形式结束。|1375433|过早优化..。(剩下的你都知道了:P+)|1375434|entityMap^0|0|0|6|2|0|A|2|E|7|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|T|8|@$F|U|G|V|H|I]]|9|@]|A|$]]|$1|J|3|K|5|6|7|W|8|@$F|X|G|Y|H|I]|$F|Z|G|10|H|I]]|9|@]|A|$]]|$1|L|3|M|5|6|7|11|8|@]|9|@]|A|$]]|$1|N|3|O|5|6|7|12|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|Q|$]]

They have different meanings.

The first example will stop when the condition is met.

The second will test <code>$x</code> twice.

You may want to make your second <code>if</code> an <code>else if</code>. This will mean the block will be skipped as soon as one condition evaluates to true.

But if you are wondering which one is fastest, you should instead think which one most effectively communicates what I want to do. They will both most probably end up as conditional jumps in the target architecture.

Premature optimisation... (you know the rest :P )

blocks|key|3713293|text|当有两个以上的选择时，切换更好。它主要是为了代码的可读性和可维护性，而不是性能。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3713294|然而，正如其他人所指出的，你的例子并不等同。|3713295|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|$]]

Switch is better when there are more than two choices. It's mostly for code readability and maintainability rather than performance. 

As others have pointed out, your examples aren't equivalent, however.

blocks|key|3713390|text|switch语句会更快，因为它只检查一次值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3713391|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|$]]

The switch statement will be faster because it only checks the value once.

blocks|key|3713167|text|首先，你所拥有的是不一样的|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3713168|switch(value)
++case+condition1:
++++break;
++case+condition2:
++++break

if+(condition1)+{
}
if+(condition2)+{
}|code-block|syntax|javascript|3713169|3713170|这些是同义词|3713171|switch(value)
++case+condition1:
++++break;
++case+condition2:
++++break

if+(condition1)+{
}
else+if+(condition2)+{
}|3713172|3713173|第二，如果你在谈论我的第二个例子，这两者是同义的。然后，在编写大量if+..else+if语句时，使用switch语句可以减轻一些痛苦。|offset|length|style|CODE|3713174|在我看来，开关还可以提供更多的可读性。但即便如此，有时使用if...else会更好，尤其是在处理复杂逻辑时。|3713175|entityMap^0|0|0|0|0|0|0|X|C|1F|6|0|T|9|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]]|$1|G|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|Z|8|@]|9|@]|A|$]]|$1|J|3|K|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|L|3|-4|5|6|7|11|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|12|8|@$O|13|P|14|Q|R]|$O|15|P|16|Q|R]]|9|@]|A|$]]|$1|S|3|T|5|6|7|17|8|@$O|18|P|19|Q|R]]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|V|$]]

First what you have is not the same

<pre><code>switch(value)
 case condition1:
 break;
 case condition2:
 break

if (condition1) {
}
if (condition2) {
}
</code></pre>

<hr>

These are synonymous

<pre><code>switch(value)
 case condition1:
 break;
 case condition2:
 break

if (condition1) {
}
else if (condition2) {
}
</code></pre>

<hr>

Second if you are talking about my second example where the two are synonymous. Then using <code>switch</code> statements can ease some pain in coding lots of <code>if ..else if</code> statements....

Switches in my point of view can also provide a bit more readability. But even then there are times when using <code>if...else</code> is simply better especially with complex logic.

blocks|key|2118111|text|如果您有一个单独的变量，一组可能的值，并且您想对每个值执行不同的操作，这就是switch-case的用途。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2118112|Switch语句更明显地表明，您只是在确定变量具有哪些允许值。|2118113|如果您有更复杂的条件，或者需要考虑多个变量，请使用If语句。|2118114|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

If you have a single variable, a set of possible values, and you want to perform different actions for each value, that's what switch-case is for.

Switch statements make it more obvious that you are merely determining which of the allowed values a variable had.

If you have more complex conditions, or multiple variables to consider, use if-statements.

blocks|key|2118183|text|这两个语句都是决策语句，通过比较某些参数，然后显示结果。switch语句无疑比if语句快，但是if语句比switch语句有更大的优势，即当您必须使用(<，>，<=，>=，!=，==)这样的逻辑操作时。每当你遇到逻辑操作时，你都会被使用switch语句去掉，但不用担心，还有另一种方法可以用来达到你的目标，那就是if-statement或if-else或if-else-if语句。我建议你在大多数情况下使用if-else，而不是switch。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2118184|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|$]]

both of the statement are decision making statement by comparing some sort of the parameters and then show the results. the switch statement is no doubt faster than the if statement but the if statement has a bigger advantage over the switch statement that is when you have to use logical operations like (&lt;,>,&lt;=,>=,!=,==). whenever you came across with the logical operations you will be struck off by using switch statement but don't worry there is another way which can be use to reach at your goal that is if-statement or if-else or if-else-if statement. I'll suggest you to use if-else most of the time rather than the switch one.

I'm in a dilemma. Which is best to use and why.. switch or if?

<pre><code>switch ($x) 
{
case 1:
 //mysql query 
 //echo something
 break;
case 2:
 //mysql query 
 //echo something
 break;
}
</code></pre>

...

<pre><code>if ($x == 1) {
 //mysql query 
 //echo something 
} 

if ($x == 2) { 
 //mysql query 
 //echo something
} 
</code></pre>

Switch vs if statements

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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我进退两难。哪一个是最好的，为什么..切换还是if？switch ($x) {case 1:  //mysql query   //echo something  break;case 2:  //mysql query   //echo something  break;}..。if ($x == 1) {    //mysql query     //echo something    } i

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