初试牛刀121205

「爱情、让人受尽委屈。」 2022-05-13 06:42 159阅读 0赞

输入一句话，再输入刚才那句话中你想更改的字符串，然后输入要替换的字符串，然后输出。

以下是自己看了书上的例子，自己写的代码，结果悲剧。

#include <iostream>
    #include <string>
    
    using namespace std;
    
    int main()
    {
    	string text;
    	cout << "Enter a string terminated by #:  " << endl;
    	getline(cin, text, '#');
    
    	string word;
    	cout << "Enter the word to be replaced:  " << endl;
    	cin >> word;
    
    	string replacement;
    	cout << "Enter the replacement word:  " << endl;
    	cin >> replacement;
    
    	if (word == replacement)
    		cout << "The word and its replacement are the same.  " << endl;
    	
    	size_t start = text.find(word);
    
    	while (start != string::npos)
    	{
    		text.replace(start, word.length(), replacement);
    		cout << "Your string is now: " << text <<endl;
    
    	};
    
    
    	return 0;
    }

输出结果惊人：（无法上图，算了，总之是一个循环无限下去）

![Image 1][]

如果输入的待更改字符串与替换字符串相同的话，即word == replacement：

![Image 1][]

所以对照一下书上代码，发现症结所在。

**第一个问题**；while循环中，首先看条件，只要start不等于string::npos就一直循环，问题就出在这里了，为什么它会一直搞下去，因为，没有检测到string::npos。所以应该在循环中加入一个递增，这也是**基本常识**。

<table> 
 <tbody> 
  <tr> 
   <td> <p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; start = text.find(word, start + replacement.length());</p> </td> 
  </tr> 
 </tbody> 
</table>

还有，需要把while循环中的输出写到结尾，如果text中有多个要替换的word输出会出现多个渐变的输出结果，而我们需要的是最后一个结果。

<table> 
 <tbody> 
  <tr> 
   <td> <p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; text.replace(start, word.length(), replacement);</p> <p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <strong>cout &lt;&lt; "Your string is now: " &lt;&lt; text &lt;&lt;endl;</strong></p> <p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; start = text.find(word, start + replacement.length());</p> </td> 
  </tr> 
 </tbody> 
</table>

第二个问题；同样if循环中，既然出错了就需要一个终止。

<table> 
 <tbody> 
  <tr> 
   <td> <p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; cout &lt;&lt; "The word and its replacement are the same.&nbsp; " &lt;&lt; endl;</p> <p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <strong>exit(1);</strong></p> </td> 
  </tr> 
 </tbody> 
</table>

最终代码更改以后

#include <iostream>
    #include <string>
    
    using namespace std;
    
    int main()
    {
    	string text;
    	cout << "Enter a string terminated by #:  " << endl;
    	getline(cin, text, '#');
    
    	string word;
    	cout << "Enter the word to be replaced:  " << endl;
    	cin >> word;
    
    	string replacement;
    	cout << "Enter the replacement word:  " << endl;
    	cin >> replacement;
    
    	if (word == replacement)
    	{
    		cout << "The word and its replacement are the same.  " << endl;
    		exit(1);
    	}
    	
    	size_t start = text.find(word);
    
    	while (start != string::npos)
    	{
    		text.replace(start, word.length(), replacement);
    		start = text.find(word, start + replacement.length());
    
    	}
    
    	
    	cout << "Your string is now: " << text <<endl;
    
    
    	return 0;
    }

得以实现—— **牛刀小试，以失败告终！！**

[Image 1]: