条件语句
C#拥有两个条件语句的构造器:
- if语句可以用来判断指定条件是否满足;
- switch语句则比较表达式可能产生的多个结果值,switch / case 语句提供了一种更方便的多分支条件选择;
if语句
using System; namespace Wrox { internal class Program { private static void Main() { Console.WriteLine("Type in a string"); string input; input = Console.ReadLine(); if (input == "") { Console.WriteLine("You typed in an empty string."); } else if (input.Length < 5) { Console.WriteLine("The string had less than 5 characters."); } else if (input.Length < 10) { Console.WriteLine( "The string had at least 5 but less than 10 Characters."); } Console.WriteLine("The string was " + input); } } }
注意:作为if的判断条件,只能是true或者false或者返回true/false的表达式,C#不允许使用整型代替。
Switch语句
switch (integerA) { case 1: Console.WriteLine("integerA = 1"); break; case 2: Console.WriteLine("integerA = 2"); break; case 3: Console.WriteLine("integerA = 3"); Console.WriteLine("integerA is not 1 or 2."); break; default: Console.WriteLine("integerA is not 1, 2, or 3"); break; }
注
- 当任何case都不满足表达式条件时,就会进入default里执行;
- case之后的值必须是常量,不能是表达式,也不能是任何变量;
- C#可以将2个或者多个case语句进行同一种处理
switch(country) { case "au": case "uk": case "us": language = "English"; break; case "at": case "de": language = "German"; break; }