1.正则表达

如果字符串是混合模式，即同时含有不同的类型，可以使用以下的方法分割他们的元素。

using System;using System.Text.RegularExpressions;public class Example{   public static void Main()   {      String[] expressions = { "16 + 21", "31 * 3", "28 / 3",                               "42 - 18", "12 * 7",                               "2, 4, 6, 8" };      String pattern = @"(\d+)\s+([-+*/])\s+(\d+)";      foreach (var expression in expressions)         foreach (Match m in Regex.Matches(expression, pattern)) {            int value1 = Int32.Parse(m.Groups[1].Value);            int value2 = Int32.Parse(m.Groups[3].Value);            switch (m.Groups[2].Value)            {               case "+":                  Console.WriteLine("{0} = {1}", m.Value, value1 + value2);                  break;               case "-":                  Console.WriteLine("{0} = {1}", m.Value, value1 - value2);                  break;               case "*":                  Console.WriteLine("{0} = {1}", m.Value, value1 * value2);                  break;               case "/":                  Console.WriteLine("{0} = {1:N2}", m.Value, value1 / value2);                  break;            }         }   }}// The example displays the following output://       16 + 21 = 37//       31 * 3 = 93//       28 / 3 = 9.33//       42 - 18 = 24//       12 * 7 = 84

\s-

Match a whitespace character followed by a hyphen.

\s?

Match zero or one whitespace character.

[+*]?

Match zero or one occurrence of either the + or * character.

\s?

Match zero or one whitespace character.

-\s

Match a hyphen followed by a whitespace character.

using System;using System.Text.RegularExpressions;public class Example{   public static void Main()   {      String input = "[This is captured\ntext.]\n\n[\n" +                     "[This is more captured text.]\n]\n" +                     "[Some more captured text:\n   Option1" +                     "\n   Option2][Terse text.]";      String pattern = @"\[([^\[\]]+)\]";      int ctr = 0;      foreach (Match m in Regex.Matches(input, pattern))         Console.WriteLine("{0}: {1}", ++ctr, m.Groups[1].Value);   }}// The example displays the following output://       1: This is captured//       text.//       2: This is more captured text.//       3: Some more captured text://          Option1//          Option2//       4: Terse text.

Match an opening bracket.

([^\[\]]+)

Match any character that is not an opening or a closing bracket one or more times. This is the first capturing group.

Match a closing bracket.

2.搜索指定的字符

using System;using System.Collections.Generic;public class Example{   public static void Main()   {      String value = "This is the first sentence in a string. " +                     "More sentences will follow. For example, " +                     "this is the third sentence. This is the " +                     "fourth. And this is the fifth and final " +                     "sentence.";      var sentences = new List
     
      ();      int position = 0;      int start = 0;      // Extract sentences from the string.      do {         position = value.IndexOf('.', start);         if (position >= 0) {            sentences.Add(value.Substring(start, position - start + 1).Trim());            start = position + 1;         }      } while (position > 0);      // Display the sentences.      foreach (var sentence in sentences)         Console.WriteLine(sentence);   }}// The example displays the following output://       This is the first sentence in a string.//       More sentences will follow.//       For example, this is the third sentence.//       This is the fourth.//       And this is the fifth and final sentence.

IndexOf , 返回某个特定字符或者字符串第一次出现的位置，which returns the zero-based index of the first occurrence of a character or string in a string instance.

IndexOfAny , 返回某个或多个特定字符或者字符串第一次出现的位置，which returns the zero-based index in the current string instance of the first occurrence of any character in a character array.

LastIndexOf ,返回某个特定字符或者字符串最后一次出现的位置，which returns the zero-based index of the last occurrence of a character or string in a string instance.

LastIndexOfAny, which returns a zero-based index in the current string instance of the last occurrence of any character in a character array.

string.IndexOf/string.LastIndexOf

IndexOf方法用于搜索在一个字符串中，某个特定的字符或者子串第一次出现的位置，该方法区分大小写，并从字符串的首字符开始以0计数。如果字符串中不包含这个字符或子串，则返回-1。

定位字符：

int IndexOf(char value)

int IndexOf(char value, int startIndex)

int IndexOf(char value, int startIndex, int count)

定位子串：

int IndexOf(string value)

int IndexOf(string value, int startIndex)

int IndexOf(string value, int startIndex, int count)