条件执行语句

if语句

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if (<test>)
{
    <code executed if <test> is true>;
}
else
{
    <code executed if >test> is false>;
}

if…else语句

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if (var1 == 1)
{
    // Do somthing
}
else if (var1 < 1)
{
    // Do somthing
}
else
{
    // Do somthing
}
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if (var1 == 1)
{
    // Do somthing.
}
else
{
    if (var < 1)
    {
        // Do somthing
    }
    else
    {
        // Do somthing
    }
}

switch语句

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switch (<testVal>)
{
    case <comparisonVal1>:
        <code to execute if <testVal> == <comparisonVal1>>;
        break;
    case <comparisonVal2>；
        <code to execute if <testVal> == <comparisonVal2>>;
        break;
    ...
    default:
        <code to execute if <testVal> != <comparisionVals>;
        break;
}
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for( int x=1; x<6; x++ ) 
{ 
	switch( x ) 
	{ 
		case 2: 
			Console.WriteLine($"x is { x } -- In Case 2"); 
			break; 
		case 5: 
			Console.WriteLine($"x is { x } -- In Case 5"); 
			break; 
		default: 
			Console.WriteLine($"x is { x } -- In Default case"); 
			break; 
	} 
}
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x is 1 -- In Default case 
x is 2 -- In Case 2 
x is 3 -- In Default case 
x is 4 -- In Default case 
x is 5 -- In Case 5

循环语句

while语句

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while (<Test>)
{
    <code to looped>
}

do循环

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do
{
    <code to be looped>
} while(<Test>);

for循环

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for(<initialization>; <condition>; <operation>)
{
    <code to loop>
}

等价于

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<initialization>;
while(<condition>)
{
    <code to loop>;
    <operation>;
}

for语句中变量的作用域

初始化和迭代表达式中的多表达式

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static void Main()
{
	const int MaxI = 5;
	for(int i = 0m, j = 10; i < MaxI; i++, j += 10)
	{
		Console.WriteLine($"{i}, {j}");
	}
}

跳转语句

  • break：立即终止循环
  • continue：立即终止当前的循环（执行下一次循环）
  • return：跳出循环及包含该循环的函数

break语句

continue语句

goto语句

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bool thingsAreFine; 
while (true) 
{ 
	thingsAreFine = GetNuclearReactorCondition(); 
	if (thingsAreFine) 
		Console.WriteLine("Things are fine."); 
	else 
		goto NotSoGood; 
} 

NotSoGood: Console.WriteLine("We have a problem.");

using语句

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using System; //using 指令，不是 using 语句 
using System.IO; //using 指令，不是 using 语句 

namespace UsingStatement 
{ 
	class Program 
	{ 
		static void Main() 
		{ 
			//using 语句 
			using (TextWriter tw = File.CreateText("Lincoln.txt")) 
			{ 
				tw.WriteLine("Four score and seven years ago, ..."); 
			} 
			
			//using 语句 
			using (TextReader tr = File.OpenText("Lincoln.txt")) 
			{ 
				string InputString; 
				while (null != (InputString = tr.ReadLine())) 
					Console.WriteLine(InputString); 
			} 
		} 
	} 
}

其他语句

语句 描述
checked、unchecked 控制溢出检查上下文
foreach 遍历一个集合的每个成员
try、throw、finally 处理异常
return 将控制返回到调用函数的成员，而且还能返回一个值
yield 用于迭代