blocks|key|1360811|text|当你需要做一件事至少做一次，但不知道在启动循环之前的次数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1360812|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|$]]

When you need something done at least once, but don't know the number of times prior to initiating the loop.

blocks|key|4211007|text|这通常不是最好的选择，但有一种情况是，你必须至少做一次某件事，但任何进一步的迭代都取决于某些条件。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4211008|do+{
++++//do+something
}+while+(+condition+);|code-block|syntax|javascript|4211009|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|$]]

It's not often that it's the best thing to use, but one scenario is when you must do something at least once, but any further iterations are dependent on some condition.

<pre><code>do {
 //do something
} while ( condition );
</code></pre>

blocks|key|993020|text|还没有人提到它在C宏中的用法...|type|unstyled|depth|inlineStyleRanges|entityRanges|data|993021|#define+do_all(x)+do{+foo(x);+bar(x);+baz(x);+}+while(0)|code-block|syntax|javascript|993022|然后在代码中你可以拥有|993023|do_all(a);|993024|993025|这一点是因为它只执行了一次，宏调用末尾的分号完成了while(0)；语句。|unordered-list-item|993026|993027|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|T|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|V|8|@]|9|@]|A|$]]|$1|L|3|M|5|N|7|W|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|X|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|Q|$]]

No-one's yet mentioned its use in C macros...

<pre><code>#define do_all(x) do{ foo(x); bar(x); baz(x); } while(0)
</code></pre>

then in the code you can have

<pre><code>do_all(a);
</code></pre>

<ul>
<li>the point being that it gets executed exactly once and the semi-colon on the end of the macro call completes the while(0); statement.</li>
</ul>

blocks|key|4211212|text|如果我需要实现很多条件检查，比如在php中处理输入表单，我以前就用过它。可能不是最佳实践，但它比许多替代方法更具可读性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4211213|do+{
+++if+(+field1_is_invalid+)+{
++++++$err_msg+=+"field1+is+invalid";+break;
+++}

+++if+(+field2_is_invalid+)+{
++++++$err_msg+=+"field2+is+invalid";+break;
+++}

+++..+check+half+a+dozen+more+things+..

+++//+Only+executes+if+all+checks+succeed.
+++do_some_updates();

}+while+(false)|code-block|syntax|javascript|4211214|另外，我猜从技术上讲这不是一个循环。更像是一种避免使用GOTO的方法:)|4211215|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I've used it before if I need to implement lots of conditional checks, for example processing an input form in php. Probably not the best practice, but it's more readable than many alternatives:

<pre><code>do {
 if ( field1_is_invalid ) {
 $err_msg = "field1 is invalid"; break;
 }

 if ( field2_is_invalid ) {
 $err_msg = "field2 is invalid"; break;
 }

 .. check half a dozen more things ..

 // Only executes if all checks succeed.
 do_some_updates();

} while (false)
</code></pre>

Also, I guess this isn't technically a loop. More like a way of avoiding using GOTO :)

blocks|key|1361007|text|当一些事情需要发生时，我通常使用do-while，但它不一定会在第一次发生时“正确”发生。例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1361008|int+x;
do
{
++++x+=+random.next(100);
++++cout+<<+x+<<+endl;
}+while+(x+!=+13);|code-block|syntax|javascript|1361009|在这种情况下，开头的x一点也不重要，因为它被覆盖了。|1361010|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

I usually use a do-while when something needs to happen, but it won't necessarily happen "correctly" on the first time. For instance:

<pre><code>int x;
do
{
 x = random.next(100);
 cout &lt;&lt; x &lt;&lt; endl;
} while (x != 13);
</code></pre>

In this case, the x you start with doesn't matter at all, because it's overwritten.

blocks|key|992676|text|当您希望在循环执行结束时检查您的条件时，这是合适的。因此，循环将始终至少运行一次，然后它将验证是否应该进一步迭代。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|992677|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|$]]

It's appropriate when you would like to have your condition checked at the end of the loop execution. Hence the loop will always run at least once and then it will verify if it should iterate further.

blocks|key|4211047|text|如果更适合做一些事情，然后将boolean+expression...or求值为Brian+said...when，那么您至少需要做一次。此语法将布尔表达式的求值移动到循环之后，而不是循环之前。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4211048|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|$]]

When it is more appropriate to do something and then evaluate the boolean expression...or as Brian said...when you need something done at least once. This syntax moves the evaluation of the boolean expression to after the loop instead of before the loop.

blocks|key|1360890|text|每当循环中的内容需要至少执行一次时。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1360891|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|$]]

Whenever what is in the loop needs to be executed at least once.

blocks|key|1360903|text|长期以来，我一直认为do-while在基于C的语言中没有得到应有的使用，因为"while“关键字的重用是笨拙和令人困惑的。Pascal的repeat-until不与while-begin-end结构共享任何关键字。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1360904|我希望有一天能分析一大堆代码，看看与其他语言中的类似结构相比，do-while在C代码中的表现是否不足。|1360905|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|$]]

I've long held that do-while is not used in C-based languages as much as it should be because the reuse of the "while" keyword is awkward and confusing. Pascal's repeat-until does not share any keywords with its while-begin-end structure.

I'd love to analyze a big heap of code someday and see if do-while is underrepresented in C code compared to similar constructs in other languages.

blocks|key|1360976|text|do+while()在条件为true时循环，但另一方面，Pascal的repeat+until在条件为false时循环(两者都将至少运行一次)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|BOLD|entityRanges|data|1360977|当我用Pascal编程时，我几乎总是使用repeat+until。|1360978|当我在C%2B%2B中编程时，我几乎总是使用while()+{}。|1360979|我不能解释为什么，但我觉得这很正常。奇怪吗？|1360980|entityMap^0|0|A|Z|C|E|4|1F|5|0|K|C|0|I|A|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|D]|$9|V|A|W|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|X|8|@$9|Y|A|Z|B|C]]|E|@]|F|$]]|$1|I|3|J|5|6|7|10|8|@$9|11|A|12|B|C]]|E|@]|F|$]]|$1|K|3|L|5|6|7|13|8|@]|E|@]|F|$]]|$1|M|3|-4|5|6|7|14|8|@]|E|@]|F|$]]]|N|$]]

<code>do while()</code> loops while a condition is true, but on the other hand, Pascal's <code>repeat until</code> loops while a condition is false (both will run at least once).

When I program in Pascal I almost always use <code>repeat until</code>. 
When I program in C++ I almost always use <code>while() {}</code>. 
I can't explain why, but I feel it's normal. Weird?

blocks|key|1361028|text|当从文件读取或等待建立连接(也是其他人类交互)时，任何迭代次数都是先验未知的(例如，sql查询返回的记录数)，或者当您执行不同大小的步骤时(例如，根据最后一次读取从文件中读取1行或5行)，当遍历对象的所有组合/排列时，无论何时“for”循环条件变得繁琐|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1361029|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|$]]

when reading from a file or waiting for a connection to be established (other human interaction as well), anything for what the number of iterations is not known a priori (e.g. number of records returned by an sql query), or when you do steps of different size (e.g. read 1 or 5 lines from the file depending on the last one read), when going over all combinations/permutations of objects, whenever 'for' loop conditions become cumbersome

blocks|key|4211503|text|执行递归操作时的另一个异常，例如下面读取内部异常时的情况：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4211504|catch(Exception+exc)
{
++++Exception+currentException+=+exc;
++++do
++++{
++++++++Console.WriteLine(string.Format("{0}:+{1}",+currentException.GetType().Name,+currentException.Message));
++++}+while((currentException+=+currentException.InnerException)+!=+null);
}|code-block|syntax|javascript|4211505|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|$]]

Another exception when you are doing something recursive, like the following with reading inner exceptions:

<pre><code>catch(Exception exc)
{
 Exception currentException = exc;
 do
 {
 Console.WriteLine(string.Format("{0}: {1}", currentException.GetType().Name, currentException.Message));
 } while((currentException = currentException.InnerException) != null);
}
</code></pre>

blocks|key|1359992|text|通常，当您需要用户输入一些值时，计数器变量基于输入值，您可以使用do-while。//以下代码是用C%2B%2B编写的。它要求用户输入一个数字并重复，直到用户输入大于0的数字。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1359993|do{
++++cout+<<+"Enter+a+Positive+integer:+";
++++cin+>>+num;
}while(+num+<+0+);|code-block|syntax|javascript|1359994|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|$]]

Normally when you need the user to input some value, the counter variable is based on the input value, you use do-while.
//The following code is in C++. It requires the user to input a number and repeats until users input number larger than 0.
<pre><code>do{
 cout &lt;&lt; &quot;Enter a Positive integer: &quot;;
 cin &gt;&gt; num;
}while( num &lt; 0 );
</code></pre>

When is a do-while the better choice over other types of loops? What are some common scenarios where its better than others?

I understand the function of a do-while, but not when to use it.

When is a do-while appropriate?

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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什么时候do-while比其他类型的循环更好呢？有哪些常见的场景比其他场景更好？我理解do-while的功能，但不知道何时使用它。

问什么时候do-while是合适的？
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问什么时候do-while是合适的？
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