#字符串和正则表达式.pptVIP

* * * * * * * * * * * * * * * * * * */19 JILIN UNIVERSITY College of Computer Science Technology */19 */19 */19 */19 */19 */19 */19 */19 */19 */19 9 Strings and Regular Expressions Shuai Lü 2012.9.5 0. Introduction The string keyword in C# actually refers to the System.String .NET base class. System.Text System.Text.StringBuilder IFormatProvider, IFormattable System.Text.RegularExpressions 1. System.String System.String is a class specifically designed to store a string and allow a large number of operations on the string. You can concatenate strings using operator overloads string message1 = Hello; // returns Hello message1 += , There; // returns Hello, There string message2 = message1 + !; // returns Hello, There! C# also allows extraction of a particular character using an indexer-like syntax string message = Hello; char char4 = message[4]; // returns o. Note the string is zero-indexed 1. System.String The key methods of System.String Compare, CompareOrdinal Concat, CopyTo, Insert, Join, Replace, Split, Substring Format IndexOf, IndexOfAny, LastIndexOf, LastIndexOfAny PadLeft, PadRight ToLower, ToUpper, Trim 1. System.String The String class has a shortcoming that makes it very inefficient for making repeated modifications to a given string — it is actually an immutable data type, which means that after you initialize a string object, that string object can never change. The methods and operators that appear to modify the contents of a string actually create new strings, copying across the contents of the old string if necessary. 1. System.String string greetingText = Hello from all the guys at Wrox Press. ; //39 chs greetingText += We do hope you enjoy this book as much as we enjoyed writing it.; // 39+65-1=103 chs for(int i = z; i = a; i--) { char old1 = (char)i; char new1 = (char)(i+1); greetingText = greetingText.Replace(old1, new1); } for(int i = Z; i =A; i--) … Console.WriteLine(Encoded:\n + greetingText); 2. System.Text.StringBuilder The StringBuil