如何使字符串中每个单词的第一个或最后一个字母小写[关闭]

Question

假设我们正在传递一个包含多个单词的字符串。

有没有办法让字符串中每个单词的第一个或最后一个字母为小写或大写？

我尝试了文本信息类，但它只为每个第一个字符提供大写方法。

我真的想不出如何对我自己的方法进行硬编码。

Answer 1

您可以使用这些扩展方法来放入一个名为例如StringHelper 的静态类：

    using System.Linq;

    static public string LastLetterOfWordsToLower(this string str)
    {
      if ( str == null ) return null;
      var words = str.Split(' ');
      for ( int indexWord = 0; indexWord < words.Length; indexWord++ )
      {
        string word = words[indexWord];
        if ( word != "" )
        {
          for ( int indexChar = word.Length - 1; indexChar >= 0; indexChar-- )
            if ( char.IsLetter(word[indexChar]) )
            {
              char c = char.ToLower(word[indexChar]);
              words[indexWord] = word.Substring(0, indexChar) + c;
              if ( indexChar != word.Length - 1 )
                words[indexWord] += word.Substring(indexChar + 1);
              break;
            }
        }
      }
      return string.Join(" ", words);
    }

    static public string FirstLetterOfWordsToLower(this string str)
    {
      if ( str == null ) return null;
      var words = str.Split(' ');
      for ( int indexWord = 0; indexWord < words.Length; indexWord++ )
      {
        string word = words[indexWord];
        if ( word != "" )
        {
          for ( int indexChar = 0; indexChar < word.Length; indexChar++ )
            if ( char.IsLetter(word[indexChar]) )
            {
              char c = char.ToLower(word[indexChar]);
              words[indexWord] = c + word.Substring(indexChar + 1);
              if ( indexChar != 0 )
                words[indexWord] = word.Substring(0, indexChar) + words[indexWord];
              break;
            }
        }
      }
      return string.Join(" ", words);
    }

测试：

    static public void StringHelperTest()
    {
      string[] list =
      {
        null,
        "",
        "A",
        "TEST",
        "A TEST STRING,  FOR STACK OVERFLOW!!"
      };
      foreach ( string str in list )
        Console.WriteLine(str.LastLetterOfWordsToLower());
      foreach ( string str in list )
        Console.WriteLine(str.FirstLetterOfWordsToLower());
    }

输出：

a
TESt
A TESt STRINg,  FOr STACk OVERFLOw!!


a
tEST
a tEST sTRING,  fOR sTACK oVERFLOW!!

StringBuilder 可用于解决性能问题。

Answer 2

有很多方法可以做到这一点。我建议你使用ToCharArray 方法来获取字符数组。然后，您可以遍历字符并确定哪些字符位于单词的第一个和最后一个字符并更改字母的大小写。这样你只做一次，不做任何字符串构建或连接。

以下是涵盖两种方案的示例方法以及将第一个和最后一个字符设置为较低的组合方法。对于大写字母，您只需将 ToLower 调用替换为对 ToUpper 的调用。

private static string FirstLetterOfWordToLowercase(string stringToTransform)
{
   char[] stringCharacters = stringToTransform.ToCharArray();
   for (int charIndex = 0; charIndex < stringCharacters.Length; charIndex++)
   {
      char currentCharacter = stringCharacters[charIndex];
      if (!isWordSepparator(currentCharacter))
      {
         if (charIndex == 0 || (charIndex > 0 && isWordSepparator(stringCharacters[charIndex - 1])))
         {
            stringCharacters[charIndex] = char.ToLower(currentCharacter);
         }
      }
   }
   return new string(stringCharacters);
}

private static string LastLetterOfWordToLowercase(string stringToTransform)
{
   char[] stringCharacters = stringToTransform.ToCharArray();
   for (int charIndex = 0; charIndex < stringCharacters.Length; charIndex++)
   {
      char currentCharacter = stringCharacters[charIndex];
      if (!isWordSepparator(currentCharacter))
      {
         if (charIndex == stringCharacters.Length - 1 || isWordSepparator(stringCharacters[charIndex + 1]))
         {
            stringCharacters[charIndex] = char.ToLower(currentCharacter);
         }
      }
   }
   return new string(stringCharacters);
}

private static string FirstAndLastLetterOfWordToLowercase(string stringToTransform)
{
   char[] stringCharacters = stringToTransform.ToCharArray();
   for (int charIndex = 0; charIndex < stringCharacters.Length; charIndex++)
   {
      char currentCharacter = stringCharacters[charIndex];
      if (!isWordSepparator(currentCharacter))
      {
         if (charIndex == 0 || charIndex == stringCharacters.Length - 1 // is first or last character
            || (charIndex > 0 && isWordSepparator(stringCharacters[charIndex - 1])) // previous character was a word separator
            || isWordSepparator(stringCharacters[charIndex + 1])) // next character is a word separator
         {
            stringCharacters[charIndex] = char.ToLower(currentCharacter);
         }
      }
   }
   return new string(stringCharacters);
}

private static bool isWordSepparator(char character)
{
   return char.IsPunctuation(character) || char.IsSeparator(character);
}

这里还有一个指向.NET Fiddle 的链接，您可以在其中看到它的工作原理。