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 directives using 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
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);
}
1.4