语句类别
本期介绍 goto, yield 关键字
| 类别 |
C#关键字 |
| 选择语句 |
if、else、switch、case |
| 迭代语句 |
do、for、foreach、in、while |
| 跳转语句 |
break、continue、default、goto、return、yield |
| 异常处理语句 |
throw、try-catch、try-finally、try-catch-finally |
| Checked 和 unchecked |
checked、unchecked |
| fixed 语句 |
fixed |
| lock 语句 |
lock |
goto
直接跳转到标记语句
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int val = 10;
if(val is int)
goto FoundInt;
else
goto Finish;
FoundInt:
Console.WriteLine("Found Integer");
Finish:
Console.WriteLine("Finish");
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跳转到特定的 case 标签或 default 标签。
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switch (n)
{
case 1:
break;
case 2:
goto case 1;
case 3:
goto default;
default:
break;
}
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跳出多层嵌套循环。
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for (int i = 0; i < x; i++)
{
for (int j = 0; j < y; j++)
{
if (array[i, j].Equals(myNumber))
{
goto FoundInt;
}
}
}
goto Finish;
FoundInt:
Console.WriteLine("Found Integer");
Finish:
Console.WriteLine("Finish");
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yield
yield 同时也属于上下文关键字。
yield 出现在迭代器内部。
yield return
yield return 表示下一次迭代要返回的数据
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foreach (int i in test())
{
Console.Write("{0} ", i);
}
public static IEnumerable<int> test()
{
int result = 0;
for (int i = 0; i < 10; i++)
{
result = result + i;
yield return result;
}
}
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另外一种应用,可轻松实现可枚举的对象 Cities,Users
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public static IEnumerable<string> Cities()
{
yield return "GUANGDONG";
yield return "BEIJING";
yield return "SHANGHAI";
yield return "SHENZHEN";
}
public static IEnumerable<User> Users()
{
yield return new User { UserId = "1", UserName = "GUANGDONG" };
yield return new User { UserId = "2", UserName = "BEIJING" };
yield return new User { UserId = "3", UserName = "SHANGHAI" };
yield return new User { UserId = "4", UserName = "SHENZHEN" };
}
public class User
{
public string UserName {get;set;}
public string UserId { get; set; }
}
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yield break
在遇到 yield break; 便会终止迭代。
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public static IEnumerable<string> Cities()
{
yield return "GUANGDONG";
yield return "BEIJING";
yield return "SHANGHAI";
yield break;
yield return "SHENZHEN";
}
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