blocks|key|861843|text|for语句中有三个子句。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|861844|init-stmt语句是在循环启动之前完成的，通常用于初始化迭代变量。|ordered-list-item|861845|条件表达式在每次执行循环之前都会进行测试。如果布尔表达式为false+(与while循环相同)，则不执行循环。|861846|下一个stmt语句是在主体执行之后完成的。它通常会增加一个迭代变量。|861847|861848|861849|因此，每个for循环执行结束，执行增量操作，在第4次迭代中，i的值为5，而for循环在第5次迭代中的值为5。|861850|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$]]|$1|E|3|F|5|D|7|Q|8|@]|9|@]|A|$]]|$1|G|3|H|5|D|7|R|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|S|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|T|8|@]|9|@]|A|$]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|N|$]]

There are three clauses in the for statement.

<ol>
<li>The init-stmt statement is done before the loop is started, usually
to initialize an iteration variable.</li>
<li>The condition expression is tested before each time the loop is
done. The loop isn't executed if the boolean expression is false
(the same as the while loop).</li>
<li>The next-stmt statement is done after the body is executed. It
typically increments an iteration variable.</li>
</ol>

So, end of each for loop execution, increment operation executed, and, in the 4th iteration, value of i is 5 and the for loop was broke as the value is 5 in 5th iteration.

blocks|key|861810|text|展开正在发生的事情|type|unstyled|depth|inlineStyleRanges|entityRanges|data|861811|int+i+=+0;

while(+i+<+5+)
{
+++//+body+of+for+loop

+++i%2B%2B;
}

//+i+==+5+here+as+i+must+be+greater+than+or+equal+to+5+to+break+out+of+while+loop|code-block|syntax|javascript|861812|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|$]]

unroll what's happening

<pre><code>int i = 0;

while( i &lt; 5 )
{
 // body of for loop

 i++;
}

// i == 5 here as i must be greater than or equal to 5 to break out of while loop
</code></pre>

blocks|key|861886|text|for循环是如何工作的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|861887|for+(initialization;+condition;+increment-decrement)
++++Statement|code-block|syntax|javascript|861888|运行初始化(i=0)|ordered-list-item|offset|length|style|CODE|861889|检查条件(i<5)，如果为真，则跳到3其他跳转到5|861890|Do语句({+printf("%25d\n",i)+})|861891|执行增量-递减(i%2B%2B)，跳转到2|861892|出口回路|861893|861894|861895|在上一次迭代i+==+4之前，它打印4，递增i。因此，在最后一次迭代i+==+5后，!(5+<+5)，即条件为false，退出循环。|861896|entityMap^0|0|0|6|3|0|5|3|0|5|K|0|8|3|0|0|0|0|6|6|I|1|M|1|Y|6|16|8|0^^$0|@$1|2|3|4|5|6|7|11|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|12|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|I|7|13|8|@$J|14|K|15|L|M]]|9|@]|A|$]]|$1|N|3|O|5|I|7|16|8|@$J|17|K|18|L|M]]|9|@]|A|$]]|$1|P|3|Q|5|I|7|19|8|@$J|1A|K|1B|L|M]]|9|@]|A|$]]|$1|R|3|S|5|I|7|1C|8|@$J|1D|K|1E|L|M]]|9|@]|A|$]]|$1|T|3|U|5|I|7|1F|8|@]|9|@]|A|$]]|$1|V|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]|$1|W|3|-4|5|6|7|1H|8|@]|9|@]|A|$]]|$1|X|3|Y|5|6|7|1I|8|@$J|1J|K|1K|L|M]|$J|1L|K|1M|L|M]|$J|1N|K|1O|L|M]|$J|1P|K|1Q|L|M]|$J|1R|K|1S|L|M]]|9|@]|A|$]]|$1|Z|3|-4|5|6|7|1T|8|@]|9|@]|A|$]]]|10|$]]

How does for loop works:

<pre><code>for (initialization; condition; increment-decrement)
 Statement
</code></pre>

<ol>
<li>Run initialization (<code>i=0</code>)</li>
<li>Check condition (<code>i&lt;5</code>), if true then jump to 3 else jump to 5</li>
<li>Do statement (<code>{ printf("%d\n",i) }</code>)</li>
<li>Do increment-decrement (<code>i++</code>), jump to 2</li>
<li>Exit loop</li>
</ol>

Before last iteration <code>i == 4</code>, then it prints <code>4</code>, increments <code>i</code>. Therefore after last iteration <code>i == 5</code>, <code>!(5 &lt; 5)</code>, i.e. condition is false, exit from loop.

blocks|key|864226|text|在每次迭代结束时，循环索引都会增加。然后，程序检查是否运行另一个循环。它会发现"no索引太大，并且失败了条件“，因此它不执行和退出。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|864227|除非指数太大，否则条件不会失败。它必须变得太大(这样循环就不会执行)。|864228|这就是为什么..。|864229|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|$]]

At the end of each iteration, the loop index is incremented. Then the program checks whether to run another loop. It finds "no the index is too big and fails the condition", so it doesn't execute and exits.

Until the index gets too big, the condition doesn't fail. It HAS to get too big (so the loop doesn't execute).

And that is why...

blocks|key|861819|text|因为在第4循环之后：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|861820|执行i%2B%2B，i变为5|ordered-list-item|offset|length|style|CODE|861821|i<5被计算为false|861822|因此，循环退出。|861823|861824|861825|然后在循环结束后得到i==5。|861826|实际上，在每个循环之后，在检查退出条件i<5之前，会对i<5进行评估。|861827|entityMap^0|0|2|3|6|1|0|0|3|7|5|0|0|0|0|A|4|0|J|3|R|3|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@$E|W|F|X|G|H]|$E|Y|F|Z|G|H]]|9|@]|A|$]]|$1|I|3|J|5|D|7|10|8|@$E|11|F|12|G|H]|$E|13|F|14|G|H]]|9|@]|A|$]]|$1|K|3|L|5|D|7|15|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|16|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|17|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|18|8|@$E|19|F|1A|G|H]]|9|@]|A|$]]|$1|Q|3|R|5|6|7|1B|8|@$E|1C|F|1D|G|H]|$E|1E|F|1F|G|H]]|9|@]|A|$]]|$1|S|3|-4|5|6|7|1G|8|@]|9|@]|A|$]]]|T|$]]

Because after the 4th loop:

<ol>
<li><code>i++</code> is performed, <code>i</code> becomes 5</li>
<li><code>i&lt;5</code> is evaluated as <code>false</code></li>
<li>Thus the loop exits</li>
</ol>

And then you get <code>i==5</code> after the end of loop.

Indeed, after each loop, <code>i++</code> is evaluated before checking for the exit condition, <code>i&lt;5</code>.

blocks|key|1694307|text|for+(int+i+=+0;+i+<+5;+%2B%2Bi)是这样的：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1694308|i+<-+0|ordered-list-item|1694309|检查i+<+5+(如果是)循环，否则停止|1694310|做循环|1694311|i+<-+i+%2B+1|1694312|进入步骤2|1694313|1694314|1694315|entityMap^0|0|R|0|0|6|0|2|5|0|0|0|A|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|X|8|@$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|I|3|J|5|H|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|K|3|L|5|H|7|13|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|14|8|@$9|15|A|16|B|C]]|D|@]|E|$]]|$1|O|3|P|5|H|7|17|8|@]|D|@]|E|$]]|$1|Q|3|-4|5|6|7|18|8|@]|D|@]|E|$]]|$1|R|3|-4|5|6|7|19|8|@]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1A|8|@]|D|@]|E|$]]]|T|$]]

<code>for (int i = 0; i &lt; 5; ++i)</code> goes like this:

<ol>
<li><code>i &lt;- 0</code></li>
<li>check whether <code>i &lt; 5</code>, if yes, loop, otherwise stop</li>
<li>do the loop</li>
<li><code>i &lt;- i + 1</code></li>
<li>goes to step 2</li>
</ol>

blocks|key|1725154|text|让我们看看这个循环：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1725155|for+(i+=+0;+0;+i%2B%2B)
++++do_smth();|code-block|syntax|javascript|1725156|您将看到这个循环根本不执行。因为条件从一开始就是假的。|1725157|现在|1725158|for+(i+=+0;+i+<+4;+i%2B%2B)
++++i%2B%2B;|1725159|显然，每次运行都会增加两次i+(一次在循环中，然后在，然后是，因为for的第三部分)。最后，i将具有第一个偶数值，从而使条件为假。那是6。因此，在步骤和循环外部变量的值之间没有链接。|offset|length|style|CODE|BOLD|1725160|entityMap^0|0|0|0|0|0|D|1|X|3|1A|1|1V|1|Q|4|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|X|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|Y|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|Z|8|@]|9|@]|A|$E|F]]|$1|M|3|N|5|6|7|10|8|@$O|11|P|12|Q|R]|$O|13|P|14|Q|R]|$O|15|P|16|Q|R]|$O|17|P|18|Q|R]|$O|19|P|1A|Q|S]]|9|@]|A|$]]|$1|T|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|U|$]]

Let's see this loop:

<pre><code>for (i = 0; 0; i++)
 do_smth();
</code></pre>

You'll see that this loop doesn't execute at all. Because the condition is false even from the beginning.

Now

<pre><code>for (i = 0; i &lt; 4; i++)
 i++;
</code></pre>

Clearly increases <code>i</code> twice for every run (once inside the loop and then because of the third part of the <code>for</code>). In the end, <code>i</code> will have the first even value which make the condition false. That is <code>6</code>. Thus, there is no link between the step and the value of the variable outside the loop.

I was just wondering why this :

<pre><code>int i;

for (i=0; i&lt;5; i++){

 printf("%d\n",i)

}

printf("Here i get the result that misleads me : %d\n",i)
</code></pre>

The last value is 5. 

My logic is : 

<pre><code>From 0 to 4 -&gt; printf

If i &gt; 4 (since we are dealing with integers) stop the loop.
</code></pre>

But the loop stopped at 4 not 5 ! Why do I get 5 after the loop ? Why does it ever increment ?

Arbitrary ?

Thanks,

For loop why the variable out of the loop is "last index" + step?

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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我只是想知道为什么int i;for (i=0; i<5; i++){ printf("%d\n",i)}printf("Here i get the result that misleads me : %d\n",i)最后一个值是5。我的逻辑是：From 0 to 4 -> printfIf i > 4 (since we are dealing with integers) stop t

问对于循环，为什么循环之外的变量是“最后一个索引”+步骤？
EN

回答 7

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问对于循环，为什么循环之外的变量是“最后一个索引”+步骤？EN

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问对于循环，为什么循环之外的变量是“最后一个索引”+步骤？
EN