blocks|key|2017368|text|迭代字符串并使用isupper()确定每个字符是否为大写。如果它是大写的，使用tolower()将其转换为小写。如果不是大写，使用toupper()将其转换为大写。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2017369|entityMap^0|8|9|13|9|1T|9|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

Iterate the string and use <code>isupper()</code> to determine if each character is uppercase or not. If it's uppercase, convert it to lowercase using <code>tolower()</code>. If it's not uppercase, convert it to uppercase using <code>toupper()</code>.

blocks|key|1274818|text|这里有一个不用boost就能做到的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1274819|#include+<string>
#include+<algorithm>
#include+<cctype>
#include+<iostream>

char+change_case+(char+c)+{
++++if+(std::isupper(c))+
++++++++return+std::tolower(c);+
++++else
++++++++return+std::toupper(c);+
}

int+main()+{
++++std::string+str;
++++str+=+"hEllo+world";
++++std::transform(str.begin(),+str.end(),+str.begin(),+change_case);
++++std::cout+<<+str;
++++return+0;
}|code-block|syntax|javascript|1274820|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|$]]

Here's a way to do it without boost:

<pre><code>#include &lt;string&gt;
#include &lt;algorithm&gt;
#include &lt;cctype&gt;
#include &lt;iostream&gt;

char change_case (char c) {
 if (std::isupper(c)) 
 return std::tolower(c); 
 else
 return std::toupper(c); 
}

int main() {
 std::string str;
 str = "hEllo world";
 std::transform(str.begin(), str.end(), str.begin(), change_case);
 std::cout &lt;&lt; str;
 return 0;
}
</code></pre>

blocks|key|3511463|text|您可以遍历字符串并从每个字母字符中添加或减去适当的数字，以便将ASCII值解析为大小写相反的ASCII值。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3511464|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|$]]

You can iterate through the string and add or subtract the appropriate number from each alpha character so that the ASCII value is resolved to the opposite case ASCII value.

blocks|key|2017403|text|char+*str+=+"this+is+a+test+string";
while(*str+!=+'\0')+{
++++if(*str+<=+'Z'+&&+*str+>=+'A')+{
+++++++*str+%2B=+32;
++++}
++++if(*str+>=+'a'+&&+*str+<=+'z')+{
+++++++*str+-=+32;
++++}
+str%2B%2B;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2017404|一点都不安全，只是给你一个想法。这可能对这个家庭作业很有帮助：|unstyled|2017405|​|2017406|📷|atomic|offset|length|2017407|2017408|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://i.stack.imgur.com/yDO1I.jpg|imageAlt^0|0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|Y|8|@]|9|@]|A|$]]|$1|G|3|H|5|F|7|Z|8|@]|9|@]|A|$]]|$1|I|3|J|5|K|7|10|8|@]|9|@$L|11|M|12|1|13]]|A|$]]|$1|N|3|H|5|F|7|14|8|@]|9|@]|A|$]]|$1|O|3|-4|5|F|7|15|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V|W|-4]]]]

<pre><code>char *str = "this is a test string";
while(*str != '\0') {
 if(*str &lt;= 'Z' &amp;&amp; *str &gt;= 'A') {
 *str += 32;
 }
 if(*str &gt;= 'a' &amp;&amp; *str &lt;= 'z') {
 *str -= 32;
 }
 str++;
}
</code></pre>

Not secure at all, just giving you the idea.
This might be very helpful for this homework: 

<img src="https://i.stack.imgur.com/yDO1I.jpg" alt="alt text">

blocks|key|4922756|text|您也可以翻转32位:使用ASCII字符，如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4922757|char+flipcase(char+x)
{
+++if(+::isalpha(x)+)
+++{
++++++return+x+%5E+32;
+++}
}|code-block|syntax|javascript|4922758|您也可以使用表格。然后创建一个静态表|4922759|char+flipcase(+char+x+)
{
+++return+fliptable[x];
}|4922760|后一种方法的优点是，只要它们不是多字节的，它也可以用于外部字符集-它不适用于此。无论使用哪种字符集，您都可以为wchar_t字符制作类似的表。如果字符的大小不超过2，则存储表需要少量的内存使用，尽管对于UTF-32会使用太多内存，并且查找时间很小。当然，在现实中，您将为每个具有其特征的字符存储一个小结构。|4922761|使用上面的任何一种方法，您都可以使用std::transform。|4922762|现在，真正聪明的bit:+std::transform既可以使用类(functor)，也可以使用普通函数。因此，对于多字节字符，只要替换字符始终具有相同的第一个元素，我们就可以存储状态。如果不是这样，那么转换将不会与常规迭代器一起工作。但是，您可以编写一个自定义迭代器来处理多字节字符串，该字符串将一次迭代一个可打印字符(迭代器必须取消对表示符号的多字节字符的引用)。|4922763|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|6|7|Y|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

You can flip the 32 bit as well: works with ASCII characters thus:

<pre><code>char flipcase(char x)
{
 if( ::isalpha(x) )
 {
 return x ^ 32;
 }
}
</code></pre>

You can also use a table. Create a static table then

<pre><code>char flipcase( char x )
{
 return fliptable[x];
}
</code></pre>

The latter method having the advantage of being able to be used for foreign character sets too as long as they are not multi-byte - it won't work for that. You can make a similar table for wchar_t characters with whatever character set you are using. Storing the table requires a small amount of memory use if sizeof your character is no more than 2, although it would use too much for UTF-32 and the lookup time is trivial. Of course in reality you would store a small struct for each character with its traits.

With either of the above you would use std::transform.

And now the really clever bit: std::transform can use a class (functor) as well as a plain function. For multi-byte characters we can therefore store the state as long as the replacement character will always have the same first element. If that is not the case then transform won't work with the regular iterators. However you could write a custom iterator to handle multi-byte character strings that would iterate up a printable character at a time (The iterator would have to dereference to multi-byte characters representing a symbol).

blocks|key|1274858|text|#include+<iostream>
#include+<string>
#include+<cctype>

using+namespace+std;

int+main(){
++++//Changecase+to+Uppercase
++++string+var+=+"This+is+a+String.";
++++for+(unsigned+int+i+=+0;+i+<+var.length();+i%2B%2B){
++++++++if+(islower(var[i]))
++++++++++++var[i]+=+toupper(var[i]);
++++}
++++cout+<<+var+<<+endl;
++++/*
++++Output:
++++THIS+IS+A+STRING.
++++*/
++++//Changecase+to+Lowercase
++++var+=+"This+is+a+String.";
++++for+(unsigned+int+i+=+0;+i+<+var.length();+i%2B%2B){
++++++++if+(isupper(var[i]))
++++++++++++var[i]+=+tolower(var[i]);
++++}
++++cout+<<+var+<<+endl;
++++/*
++++Output:
++++this+is+a+string.
++++*/
++++//Flip+the+case
++++var+=+"This+is+a+String.";
++++for+(unsigned+int+i+=+0;+i+<+var.length();+i%2B%2B){
++++++++if+(isupper(var[i]))
++++++++++++var[i]+=+tolower(var[i]);
++++++++else
++++++++++++var[i]+=+toupper(var[i]);
++++}
++++cout+<<+var+<<+endl;
++++/*
++++Output:
++++tHIS+IS+A+sTRING.
++++*/

++++system("pause");
++++return+0;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1274859|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>#include &lt;iostream&gt;
#include &lt;string&gt;
#include &lt;cctype&gt;

using namespace std;

int main(){
 //Changecase to Uppercase
 string var = "This is a String.";
 for (unsigned int i = 0; i &lt; var.length(); i++){
 if (islower(var[i]))
 var[i] = toupper(var[i]);
 }
 cout &lt;&lt; var &lt;&lt; endl;
 /*
 Output:
 THIS IS A STRING.
 */
 //Changecase to Lowercase
 var = "This is a String.";
 for (unsigned int i = 0; i &lt; var.length(); i++){
 if (isupper(var[i]))
 var[i] = tolower(var[i]);
 }
 cout &lt;&lt; var &lt;&lt; endl;
 /*
 Output:
 this is a string.
 */
 //Flip the case
 var = "This is a String.";
 for (unsigned int i = 0; i &lt; var.length(); i++){
 if (isupper(var[i]))
 var[i] = tolower(var[i]);
 else
 var[i] = toupper(var[i]);
 }
 cout &lt;&lt; var &lt;&lt; endl;
 /*
 Output:
 tHIS IS A sTRING.
 */

 system("pause");
 return 0;
}
</code></pre>

blocks|key|2017469|text|执行此操作的标准C%2B%2B方法如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2017470|std::string+lower+=+"this+is+my+string+to+be+uppercased";
std::locale+loc;+//get+the+locale+from+the+system.
auto+facet+=+std::use_facet<std::ctype<char>>(loc);
facet.toupper(&lower[0],+&lower[0]+%2B+lower.length());+//they+didn't+provide+a+C%2B%2B+iterator+interface,+so+pointer+arithmetic+it+is.++
std::cout+<<+lower+<<+std::endl;|code-block|syntax|javascript|2017471|这将输出以下内容：|2017472|+THIS+IS+MY+STRING+TO+BE+UPPERCASED|2017473|还有一个将小写转换为大写的facet.toupper()，以及一个从char转换为wchar_t的facet.widen，以及从wchar_t转换为char的facet.narrow。|offset|length|style|CODE|2017474|entityMap^0|0|0|0|0|D|F|1D|B|27|C|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|W|8|@$M|X|N|Y|O|P]|$M|Z|N|10|O|P]|$M|11|N|12|O|P]]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|13|8|@]|9|@]|A|$]]]|R|$]]

The standard C++ method to do this is as follows:
<pre><code>std::string lower = &quot;this is my string to be uppercased&quot;;
std::locale loc; //get the locale from the system.
auto facet = std::use_facet&lt;std::ctype&lt;char&gt;&gt;(loc);
facet.toupper(&amp;lower[0], &amp;lower[0] + lower.length()); //they didn't provide a C++ iterator interface, so pointer arithmetic it is. 
std::cout &lt;&lt; lower &lt;&lt; std::endl;
</code></pre>
this outputs:
<pre><code> THIS IS MY STRING TO BE UPPERCASED
</code></pre>
there's also a <code>facet.toupper()</code> to handle converting lowercase to uppercase, and <code>facet.widen</code> to convert from char to wchar_t, and <code>facet.narrow</code> to convert from wchar_t to char.

I have a string that may contain numbers as well as upper and lower case letters. I need to convert all the uppercase letters to lowercase and vice versa. How would one go about this?

How do I change the case of a string 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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我有一个字符串，它可以包含数字以及大小写字母。我需要将所有的大写字母转换为小写字母，反之亦然。我们该怎么做呢？

问如何在C++中更改字符串的大小写？
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