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[ASP.net教程]1、C#语言基本语句和语法


1、C#语言基本语句和语法

1.1 C#程序的基本结构和基本语法要点

Here, you’ll take a closer look at the console application example and break down the structure a bit. Here’s the code:

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;
namespace ConsoleApplication1{  class Program  {    static void Main(string[] args)    {      // Output text to the screen.      Console.WriteLine("The first app in Beginning C# Programming!");      Console.ReadKey();    }  }}

所有的C#程序后缀为.cs

编辑时,为使用代码大纲(代码折叠)功能,可如下:

#region Using directivesusing System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;#endregion

以#开头的内容可视为预指令,他不是C#的关键字。编辑时代码可折叠为1行。

区分大小写。

语句中的空格将不予考虑。

分号“;”为一条语句的结尾。一条语句可书写在2行或多行。

声明语句后面不要分号“;”

注释的方式有三种:

(1)/*                         */

特点:以“/*”开始,可书写于多行,只直到有“*/”结束。

(2)//

特点:以“//”开头,只能书写于一行。可为单独的一行,也可以放在一条语句的分号之后。

(3)///

与//相同。不同的是该方法可由VS提取内容。

占位符标签

程序中的占位符标签类似于汇编语言中的程序指针地址。下图中第2行和第1行为一个标签,因其间无分号相隔。 

<code line 1, statement 1>;<code line 2, statement 2>  <code line 3, statement 2>;

 1.2 语句

1.2.1 跳转语句

➤goto 语句

The goto statement is used as follows:

goto <labelName>;

 

Labels are defi ned as follows:
<labelName>:
For example, consider the following:

int myInteger = 5;goto myLabel;myInteger += 10;myLabel:Console.WriteLine("myInteger = {0}", myInteger);

1.2.2 分支语句

➤ The ternary operator  三元运算符
➤ The if statement     if语句
➤ The switch statement   switch语句 

1.2.2.1 三元运算符

常用于简单赋值,较复杂的代码宜用if语句。 

The syntax is asfollows:

<test> ? <resultIfTrue>: <resultIfFalse>

 Here,

<test> is evaluated to obtain a Boolean value, and the result of the operator is either <resultIfTrue> or <resultIfFalse> based on this value.
You might use this as follows to test the value of an int variable called myInteger:

string resultString = (myInteger < 10) ? "Less than 10": "Greater than or equal to 10";

如果myInteger<10,则:resultString = "Less than 10" 

如果myInteger≥10,则:resultString = "Greater than or equal to 10" 

1.2.2.2  if语句

The syntax is asfollows:

if (<test>)<code executed if <test> is true>;

 

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

 

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

举例:

static void Main(string[] args){  string comparison;  Console.WriteLine("Enter a number:");  double var1 = Convert.ToDouble(Console.ReadLine());  Console.WriteLine("Enter another number:");  double var2 = Convert.ToDouble(Console.ReadLine());  if (var1 < var2)    comparison = "less than";  else  {    if (var1 == var2)      comparison = "equal to";    else      comparison = "greater than";  }  Console.WriteLine("The first number is {0} the second number.",comparison);  Console.ReadKey();}

举例:判断更多的条件:

if (var1 == 1){// Do something.}else{if (var1 == 2){// Do something else.}else{if (var1 == 3 || var1 == 4){// Do something else.}else{// Do something else.}}}

1.2.2.3  switch语句

标准语法:The basic structure of a switch statement is as follows:

switch (<testVar>){  case <comparisonVal1>:    <code to execute if <testVar> == <comparisonVal1> >    break;  case <comparisonVal2>:    <code to execute if <testVar> == <comparisonVal2> >    break;  ...  case <comparisonValN>:    <code to execute if <testVar> == <comparisonValN> >    break;  default:    <code to execute if <testVar> != comparisonVals>    break;}

使用技巧:

{case <comparisonVal1>:  <code to execute if <testVar> == <comparisonVal1> >  goto case <comparisonVal2>;case <comparisonVal2>:  <code to execute if <testVar> == <comparisonVal2> >  break;...

switch (<testVar>){  case <comparisonVal1>:  case <comparisonVal2>:    <code to execute if <testVar> == <comparisonVal1> or    <testVar> == <comparisonVal2> >    break;  ...

switch (myInteger){  case 1:    <code to execute if myInteger == 1>    break;  case −1:    <code to execute if myInteger == −1>    break;  default:    <code to execute if myInteger != comparisons>    break;}

 1.2.3 循环语句

➤ do循环

➤ while循环

➤ for循环

➤ 循环的中断语句

无限循环

1.2.3.1 do循环 

基本语法:

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

举例:

int i = 1;do{  Console.WriteLine("{0}", i++);} while (i <= 10);

1.2.3.2 while循环

语法:

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

举例

int i = 1;while (i <= 10){  Console.WriteLine("{0}", i++);}

1.2.3.3 for循环

语法:

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

举例:

int i;for (i = 1; i <= 10; ++i){Console.WriteLine("{0}", i);}

 1.2.3.4  循环的中断语句 

➤ break — Causes the loop to end immediately
➤ continue — Causes the current loop cycle to end immediately (execution continues with the next loop cycle)
➤ goto — Allows jumping out of a loop to a labeled position (not recommended if you want your code to be easy to read and understand)
➤ return — Jumps out of the loop and its containing function (see

 1.2.3.5 无限循环

举例:

while (true){      // code in loop}

 

 1.4