blocks|key|3717441|text|简单地说(你的问题很模糊)，开关在汇编程序中编译成跳转表，因此比if+/+then+/+else更快。请注意，C中的switch语句有一个“跟随”特性(google+this)，该特性可以通过break语句绕过。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3717442|您只能打开求值为整型的对象。特别是，这意味着您不能打开字符串:字符串在任何情况下都不是自然C语言的一部分。|3717443|if+/+then+/+else连续检查几个条件。比较并不局限于整型，因为您正在测试的所有类型都是true+(不是零)或false+(零)。|3717444|这可能足以让您开始使用它。|3717445|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

Breifly (your question is vague), a switch compiles to a jump table in assembler and is therefore faster than if / then / else. Note that a switch statement in C has a 'follow-through' feature (google this) which can be circumvented with break statements. 

You can only switch on things that evaluate to integral types. In particular this means that you cannot switch on strings: strings are not part of the natural C language in any case.

An if / then / else checks several conditions in succession. Comparison is not restricted to integral types as all you're testing is true (not zero) or false (zero).

That's probably enough to get you started.

blocks|key|480467|text|当要比较的值的类型适合为switch'd，并且它使代码更具可读性时，请继续使用switch。例如，|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|480468|if+(val+==+0)+{
++++//+do+something
}+else+if+(val+==+1)+{
++++//+do+something+else
}+else+if+(val+==+2)+{
++++//+yet+another+option
}+...|code-block|syntax|javascript|480469|与switch相比，它杂乱无章，很难维护。想象一下，有一天，你不想打开val而是打开validate(val)；然后你需要改变所有的条件。|480470|此外，switch有时可能比if/else更快，因为编译器可以将其转换为jump+table或binary+search。然后，编译器可能会对一系列if/else语句执行相同的操作，尽管这是一个更难进行的优化，因为子句顺序可能很重要，而编译器必须能够检测到它并不重要。|480471|entityMap|0|LINK|mutability|MUTABLE|url|https://en.wikipedia.org/wiki/Branch_table|1|https://en.wikipedia.org/wiki/Binary_search_algorithm^0|C|6|13|6|0|0|1|6|Z|3|16|D|0|3|6|E|2|H|4|22|2|25|4|10|A|0|1B|D|1|0^^$0|@$1|2|3|4|5|6|7|Y|8|@$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]|$9|1G|A|1H|B|C]|$9|1I|A|1J|B|C]|$9|1K|A|1L|B|C]]|D|@$9|1M|A|1N|1|1O]|$9|1P|A|1Q|1|1R]]|E|$]]|$1|O|3|-4|5|6|7|1S|8|@]|D|@]|E|$]]]|P|$Q|$5|R|S|T|E|$U|V]]|W|$5|R|S|T|E|$U|X]]]]

When the value to be compared has a type that is amenable to being <code>switch</code>'d, and it makes your code more readable, then go ahead and use a <code>switch</code>. For example,

<pre><code>if (val == 0) {
 // do something
} else if (val == 1) {
 // do something else
} else if (val == 2) {
 // yet another option
} ...
</code></pre>

is cluttered and hard to maintain compared to a <code>switch</code>. Imagine that some day, you don't want to switch on <code>val</code> but on <code>validate(val)</code>; then you'd need to change all the conditions.

Also, <code>switch</code> may be faster than <code>if</code>/<code>else</code> sometimes, because a compiler may turn it into either a <a href="https://en.wikipedia.org/wiki/Branch_table" rel="nofollow">jump table</a> or a <a href="https://en.wikipedia.org/wiki/Binary_search_algorithm" rel="nofollow">binary search</a>. Then again, a compiler might do the same to a series of <code>if</code>/<code>else</code> statements, although that's a more difficult optimization to make because the clauses order might matter and the compiler must be able to detect that it doesn't.

blocks|key|479580|text|我认为If+then+else更好，只有在你只有两个条件的情况下。否则，如果条件多于2个，最好使用switch+case|type|unstyled|depth|inlineStyleRanges|entityRanges|data|479581|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 think
If then else is better in case only when you have 2 conditions only.
Otherwise its better to use switch case if conditions are more than 2

blocks|key|1621217|text|switch看起来比许多if要好，但是它只适用于数字表达式(因为char本质上是一个数字，它仍然可以应用于它，但是你不能将它与字符串一起使用)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1621218|如果我可以推荐您使用here，因为它对switch语句有一个很好的描述。注意开头的一句话：|1621219|1621220|+Switch+case语句替代了将变量与多个“整数值”(“整数值”是可以表示为整数的值，如字符的值)进行比较的长if语句。|blockquote|1621221|1621222|entityMap|0|LINK|mutability|MUTABLE|url|http://www.cprogramming.com/tutorial/lesson5.html^0|0|6|C|2|W|4|0|J|6|A|4|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|11|8|@$9|12|A|13|B|C]]|D|@$9|14|A|15|1|16]]|E|$]]|$1|H|3|-4|5|6|7|17|8|@]|D|@]|E|$]]|$1|I|3|J|5|K|7|18|8|@]|D|@]|E|$]]|$1|L|3|-4|5|6|7|19|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

<code>switch</code> looks better than lots of <code>if</code>s. However it only works on numeric expressions (as a <code>char</code> is essentially a number, it can still be applied to it, however you cannot use it with strings).

If I may point you to <a href="http://www.cprogramming.com/tutorial/lesson5.html" rel="nofollow">here</a> as it has a nice description of the <code>switch</code> statement. Note the opening sentence:

<blockquote>
 Switch case statements are a substitute for long if statements that
 compare a variable to several "integral" values ("integral" values are
 simply values that can be expressed as an integer, such as the value
 of a char).
</blockquote>

blocks|key|1594349|text|switch在性能方面也更好，因为它可以通过编译器以各种方式进行优化，这取决于值是否连续。如果是，它可以直接使用该值作为指针数组的索引。如果没有，它有时可以使用二进制搜索而不是线性搜索，当它更快的时候。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1594350|entityMap^0|0|6|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|$]]

<code>switch</code> is better performance-wise too because it can be optimized in various ways by the compiler, depending on whether the values are consecutive. If yes, it can outright use the value as an index to an array of pointers. If not, it can sometimes use a binary search instead of a linear search, when it's faster.

The question is really simple: in a laboratory class I attended this year, professor presented the <code>switch/case</code> statement alongside the classic <code>if/then/else</code> statement without saying anything about which one was better in different programming situations.

Which one is better when checking a variable which can have at least 10/15 possible values?

Differences between IF and SWITCH/CASE in C

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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问题真的很简单:在我今年参加的一堂实验课上，教授在经典的if/then/else语句旁边展示了switch/case语句，但没有说在不同的编程情况下哪一个更好。在检查一个至少可以有10/15可能值的变量时，哪一个更好？

问C语言中IF和SWITCH/CASE的区别
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