blocks|key|960934|text|C标准规定if+(expression)后面必须有一条语句。它不要求语句是复合语句。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|960935|在“C的精神”(见C的基本原理文件)中，一个短语是：|960936|相信程序员。|blockquote|960937|另一方面，MISRA对if有一个必需的规则，并循环该语句必须是一个复合语句。|960938|有些编码样式仅在语句与if放在同一行时才允许为if提供一条语句。例如：|960939|if+(condition)+statement;|code-block|syntax|javascript|960940|请注意，C和C%2B%2B不仅是使{}在if中可选的语言。例如，在Java中，它也是可选的，但在Perl中它是必需的。|960941|entityMap^0|5|F|0|0|0|B|2|0|B|2|N|2|0|0|D|2|G|2|0^^$0|@$1|2|3|4|5|6|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|10|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|11|8|@]|D|@]|E|$]]|$1|K|3|L|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|15|8|@$9|16|A|17|B|C]|$9|18|A|19|B|C]]|D|@]|E|$]]|$1|O|3|P|5|Q|7|1A|8|@]|D|@]|E|$R|S]]|$1|T|3|U|5|6|7|1B|8|@$9|1C|A|1D|B|C]|$9|1E|A|1F|B|C]]|D|@]|E|$]]|$1|V|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|W|$]]

The C Standard says that a <code>if (expression)</code> must be followed by a statement. It does not require the statement to be a compound statement.

In the "Spirit of C" (see C Rationale document), one of the phrase is:

<blockquote>
 Trust the programmer.
</blockquote>

MISRA-C on the other hand has a required rule for <code>if</code> and loops that the statement has to be a compound statement.

Some coding styles allow a single statement for <code>if</code> only if the statement is put in the same line as the <code>if</code>. For example:

<pre><code>if (condition) statement;
</code></pre>

Note that C and C++ are not only the languages to have the <code>{}</code> be optional in <code>if</code>. For example in Java it is also optional, but in Perl it is required.

blocks|key|1428450|text|有时，不必编写大括号会使代码更具可读性：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1428451|if+(x+<+0)+throw+std::invalid_argument("meh");
if+(a+!=+b)+return+0;
if+(i+==+k)+continue;|code-block|syntax|javascript|1428452|理论上，您可以设计一种编程语言来要求除了控制流语句之外的大括号，但是这种安全性可能会被额外的语言复杂性所压倒。|1428453|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|$]]

Sometimes, not having to write the braces makes the code more readable imho:

<pre><code>if (x &lt; 0) throw std::invalid_argument("meh");
if (a != b) return 0;
if (i == k) continue;
</code></pre>

In theory, you could design a programming language to require braces except for control flow statements, but this safety would probably be outweighed by the additional language complexity.

blocks|key|960996|text|作用域仅仅是一个复合语句。它可以放置在任何地方：|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|960997|void+foo()+{
++int+a+=+0;
++a+=+1;+//+this+is+a+simple+statement.
++{+//+this+is+inside+a+scope.+It+is+a+compound+statement.+Note+that+I+don't+need+an+if.
++++a+=+2;
++++a%2B%2B;
++}
++return+a;
}|code-block|syntax|javascript|960998|能够在if、while或其他构造之后放置任何语句(复合语句或非语句)，使语法的实现更加简单。|CODE|960999|entityMap^0|8|4|0|0|3|2|6|5|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|S|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|T|8|@$9|U|A|V|B|M]|$9|W|A|X|B|M]]|D|@]|E|$]]|$1|N|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|O|$]]

A scope is merely a compound statement. It can be placed anywhere:

<pre><code>void foo() {
 int a = 0;
 a = 1; // this is a simple statement.
 { // this is inside a scope. It is a compound statement. Note that I don't need an if.
 a = 2;
 a++;
 }
 return a;
}
</code></pre>

Being able to put any statement (compound or not) after an <code>if</code>, <code>while</code> or other constructs makes the syntax much simpler to implement.

blocks|key|664102|text|因为：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|664103|这将是过度干预-程序员选择编码风格，而不是语言；|unordered-list-item|664104|这将使语法更加复杂；简单地说，if+(condition)后面跟着一个statement，然后让递归处理所有事情，就更容易、更健壮了。|offset|length|style|CODE|664105|就我个人而言，对于任何能力模糊的程序员来说，对这个构造的不信任很大程度上是没有价值的；我从来没有遇到过这样的"bug“，我忘记了如何编写C%2B%2B，只是因为我选择了省略一个大括号对。如果你遇到它，我建议你把它当作一个提示，更多地关注你正在做的事情，而不是用“技巧”和“风格指南”来掩盖它。|664106|entityMap^0|0|0|F|E|Z|9|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$]]|$1|E|3|F|5|D|7|Q|8|@$G|R|H|S|I|J]|$G|T|H|U|I|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|V|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|N|$]]

Because:

<ul>
<li>that would be excessive meddling &mdash; the programmer chooses coding style, not the language;</li>
<li>it would further complicate the grammar; easier and more robust to just say that an <code>if (condition)</code> is followed by a <code>statement</code> and let the recursion handle everything.</li>
</ul>

Personally I find the distrust of this construct to be largely without merit for any vaguely competent programmer; I've not once encountered this "bug" where I've forgotten how to write C++ just because I chose to omit a brace pair. If you come across it, I suggest you treat it as a cue to pay more attention to what you're doing, rather than masking it with "tricks" and "style guides".

blocks|key|1428522|text|C是在计算机有40×25字符图形的时候创建的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1428523|如果希望对条件块/语句进行缩进，则保存1(同一行上的大括号)或两行(下一行的开头大括号)：|offset|length|style|BOLD|1428524|if+(condition)
++++statement;

if+(condition)+{
++++statement;
}

if+(condition)
{
+++statement;
}|code-block|syntax|javascript|1428525|所以节约一条线很重要。它允许在一个屏幕上显示更多的源代码。|1428526|entityMap^0|0|H|2|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|U|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

C was created in a time when computers had 40×25 character graphics.

If you want to have indentation of the condition block/statement 
you save one (opening brace on the same line) or two lines (opening brace on the following line):

<pre><code>if (condition)
 statement;

if (condition) {
 statement;
}

if (condition)
{
 statement;
}
</code></pre>

So saving a line was important. It allowed to show more source code in one screen.

blocks|key|961068|text|C/C%2B%2B也不要求严格遵守K&R风格。对于喜欢Allman风格的人来说，额外的支撑是完全没有必要的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|961069|if+(condition)
++++statement;

if+(condition)
{
+++statement;
+++statement;
}|code-block|syntax|javascript|961070|随着lambdas和支撑初始化的引入，我们在代码中看到越来越多的大括号，我认为Allman风格实际上更好地管理它。|961071|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|$]]

C/C++ also doesn't mandate strict adherence to K&amp;R style. For people who prefer Allman style, the extra braces are completely unnecessary:

<pre><code>if (condition)
 statement;

if (condition)
{
 statement;
 statement;
}
</code></pre>

With the introduction of lambdas and braced initialization, we are seeing an increasing number of braces in our code and I think Allman style actually manages it better.

blocks|key|961084|text|你有点误会了。这些大括号是，既不是可选的，也不是强制性的。没有决定是否允许或强制使用它们。大括号是，而不是if语句的部分(或任何类似的构造)。它们属于条件后面的语句。简单语句不会有它们，但是复合语句会(根据定义，复合语句是括在括号中的语句列表)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|CODE|entityRanges|data|961085|这种情况以及编译器如何处理它直接来自于这个语法定义(实际上，这个定义并不是特定于C的，我可以想到的那个时代的大多数其他语言，Algol，Pascal，不管它们使用的是关键字而不是大括号，也是如此)。基本上，任何没有特定结束关键字(如if和end+if或if和fi)的语言都必须这样处理。|961086|当您在if或任何其他类似的构造中包含单个语句的大括号时，不使用允许大括号的可选if形式。您只是碰巧为它提供了一个复合语句(因此，用大括号括起来)，其中只包含一个语句，这是完全合法的。但是对于编译器来说是一样的，它处理它没有任何不同。|961087|实际上，但这是一个品味问题，当然，许多程序员更喜欢忽略它们，因为它减少了杂乱。|961088|entityMap^0|D|G|1D|9|1H|2|0|38|2|3B|6|3I|2|3L|2|0|3|2|13|2|S|2G|0|0|13|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]|$9|T|A|U|B|D]]|E|@]|F|$]]|$1|G|3|H|5|6|7|V|8|@$9|W|A|X|B|D]|$9|Y|A|Z|B|D]|$9|10|A|11|B|D]|$9|12|A|13|B|D]]|E|@]|F|$]]|$1|I|3|J|5|6|7|14|8|@$9|15|A|16|B|D]|$9|17|A|18|B|D]|$9|19|A|1A|B|C]]|E|@]|F|$]]|$1|K|3|L|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|E|@]|F|$]]|$1|M|3|-4|5|6|7|1E|8|@]|E|@]|F|$]]]|N|$]]

You misunderstand it slightly. The braces are neither optional nor compulsory. There was no decision about whether to allow them or to enforce them at all. The braces are not part of the <code>if</code> statement (or any similar construct). They belong to the statement that follows the condition. Simple statements will not have them but compound statements will (by definition, a compound statement is a list of statements enclosed in braces).

This situation and how the compiler handles it comes directly from this syntax definition (which is, actually, nothing C-specific, most other languages of the era that I can think of, Algol, Pascal, whatever, even if they used keywords instead of braces, do the very same). Basically, any language that has no specific ending keywords (like <code>if</code> and <code>end if</code> or <code>if</code> and <code>fi</code>) have to handle it this way.

When you do include the braces around a single statement in an <code>if</code> or any other similar construct, you don't use an optional form of <code>if</code> allowing braces. You just happen to provide it with a compound statement (hence, enclosed in braces) consisting only of a single statement inside, and this is perfectly legal. But it's the same for the compiler, it doesn't handle it any different.

Actually, but this is a question of taste, of course, many programmers prefer to omit them because it reduces clutter.

Most of us have probably encountered the bug of when you add another statement inside an 'if' and notice that it prints regardless of the condition of the branch, only to find out sooner or later in frustration that the braces around the 'if' condition was missing. 

Example:

<pre><code>if (condition) {
 statement;
}
</code></pre>

Compared to:

<pre><code>if (condition)
 statement;
</code></pre>

Please note that I wouldn't want a discussion on what coding standard is better, as we all have our opinion about that and it's very much dependent on context. Instead, I would be interested in the advantages from a programming language point of view and from these advantages, why it was decided not to be strictly enforced. Does it make for a simpler grammar? Compiler implementation?

What is the advantage of leaving it optional, rather than strictly enforcing it? What does the standard say about it?

Why does C allow leaving out braces around blocks?

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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我们中的大多数人可能都遇到了错误，当您在“if”中添加另一条语句时，注意到不管分支的条件如何，它都会打印，但是迟早会发现'if‘条件周围的大括号丢失了。示例：if (condition) {    statement;}与之相比：if (condition)    statement;请注意，我不想讨论什么编码标准更好...

问为什么C允许忽略块周围的支撑？
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问为什么C允许忽略块周围的支撑？EN