第1篇 C#語言基本語句和語法
前言：本資料根據【1】整理知識要點，其內容應當是全面的。可供查閱、復習參考。
參考資料：
【1】《BEGINNING VISUAL C#® 2012 PROGRAMMING》
【2】C# 語句大全!
1、 C#程序基本結構和語法要點
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(); } } }
（1）所有的C#程序后綴為.cs
（2）編輯時，為使用代碼大綱（代碼折疊）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#開頭的內容可視為預指令，他不是C#的關鍵字。編輯時代碼可折疊為1行。
（3）區分大小寫。
（4）語句中的空格將不予考慮。
（5）分號“；”為一條語句的結尾。一條語句可書寫在2行或多行。
（6）聲明語句后面不要分號“；”
（7）注釋的方式有三種：
➤ /* */
/* */
特點：以“/*”開始，可書寫於多行，只直到有“*/”結束。
➤ //
//
特點：以“//”開頭，只能書寫於一行。可為單獨的一行，也可以放在一條語句的分號之后。
➤ ///
///
與//相同。不同的是該方法可由VS提取內容。
（8）占位符標簽
程序中的占位符標簽類似於匯編語言中的程序指針地址。下圖中第2行和第1行為一個標簽，因其間無分號相隔。
<code line 1, statement 1>; <code line 2, statement 2> <code line 3, statement 2>;
➤ 關於類、接口、Sub子程序和變量修飾符
類，以某種參數實例化后即成為對象。我這樣理解：對象就是程序中的實體，一個UI或一個數據結構，類是一些實體的共有屬性的集合。類可以通過XAML標記語言編程設計而定義，這種類一般用作UI或UI元素；類也可以通過C#代碼編程設計而定義，通過C#代碼，既可以定義用作UI或UI元素的類，可以定義數據結構的類。UI或UI元素的類不是本篇討論的內容。
C#編程與匯編語言編程完全不同。后者是為CPU編寫代碼，程序是順序結構，設計人員要用的是CPU。C#語言編程不是順序結構，基本與CPU無關，用的是微軟的操作系統，運行時，不是C#代碼在運行，而是操作系統在運行，C#代碼為操作系統提供一些任務，由微軟操作系統完成。這些代碼必須符合微軟操作系統的規定，微軟把這些規定商業包裝成.Net，為便於編程者使用.net，微軟設計了WPF、XAML、C#三個東西，你就是用這三樣東西來設計你的應用程序。XAML用於設計UI，C#代碼負責UI所體現的信息的處理。UI上產生“事件”，C#代碼處理事件，微軟稱此對事件處理的程序為“方法”，方法就是一個個的sub子程序。
定義變量的場合因此有三處，類的內外，sub的內外。類型則有臨時有效或永久有效。C#通過變量修飾符為變量設定類型。
2、 名稱空間、類和接口
2.1 定義和使用名稱空間
➤ namespace語句。定義名稱空間。語法：
namespace LevelOne
{
// code in LevelOne namespace
// name "NameOne" defined } // code in global namespace
➤ using語句。使用名稱空間。語法：
using System;
using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading.Tasks; namespace ConsoleApplication1 { ... }
2.2 定義類、聲明類的屬性
➤ internal。該修飾符聲明類是內部的，僅本項目使用。可省略。
internal class MyClass
{
// Class members.
}
➤ public。聲明類是公共的，可由其他項目中的代碼來訪問。
public class MyClass
{
// Class members.
}
➤ abstract。抽象類。不能實例化，只能繼承。下例中public亦可為internal。
public abstract class MyClass
{
// Class members, may be abstract.
}
➤ sealed。密封類。不能繼承。下例中public亦可為internal。
下例為定義一個密封類。
public sealed class MyClass
{
// Class members.
}
下例為使用一個密封類。
public class MyClass : MyBase
{
// Class members.
}
注意，在C#的類定義中，只能有一個基類。如果繼承了一個抽象類，該派生類除非也是抽象的，就必須實現繼承該抽象類的所有抽象成員。編譯器不允許派生類訪問高於該基類的類。也就是說，內部類可繼承於一個公共基類，但公共基類不能繼承於一個內部類。
在類的繼承層次結構中，所有的類的根都是System.Object。如果沒有使用基類，則所定義的類就只繼承於基類System.Object。
➤ 為類指定接口。語法：
[public] class MyClass :[ MyBase, ]IMyInterface[, IMySecondInterface][, ...]
{
// Class members.
}
2.3 定義接口、聲明接口的屬性
➤ public interface 下例：定義一個接口。
接口修飾符為public或internal；無abstract和sealed。接口無根。
[public ]interface IMyInterface
{
// Interface members.
}
➤ 接口繼承。下例：定義一個接口，該接口可以繼承於多個接口。
public interface IMyInterface : IMyBaseInterface, IMyBaseInterface2
{
// Interface members.
}
3、 變量和表達式
3.1 變量
3.1.1 變量命名要點
（1）必須以字母、下划線或@開頭，其后可為字母、下划線或數字。
（2）禁用關鍵字。
（3）區分大小寫。
（4）流行的匈牙利命名法，不同類型前以同一前綴。或以作用區分作前綴，但不適合協同編程。
（5）微軟建議對於簡單的變量使用camelCase命名法,對於高級的使用PascalCase命名法。
3.1.2 聲明變量
➤ 聲明一個變量
<type> <name>;
<type>：變量的類型（見<type>可選的內容和含義）；<name>：用戶定義的變量的名稱。
➤ 聲明多個變量，用逗號隔開
int xSize, ySize;
3.1.3 為變量賦值
➤ 為一個變量賦值
int myInteger;
string myString; myInteger = 17; myString = "\"myInteger\" is";
int xSize, ySize = 5;
xSize使用前尚需初始化
➤ 為多個變量賦值
int xSize = 4, ySize = 5;
3.1.4 變量的作用域關鍵字
➤ 全局變量和局部變量
3.2 字面值
表達式由運算符和操作數組成。變量和字面值，稱為操作數。運算符包括數學運算法、邏輯運算符和賦值運算符。運算符按照操作數的數量又分：
➤ Unary — Act on single operands 一元運算符（一個操作數）
➤ Binary — Act on two operands 二元運算符（二個操作數）
➤ Ternary — Act on three operands 三元運算符（三個操作數）
3.2.1 變量的字面值
➤ 字面值后綴
許多變量的字面值，在字符后面添加一些后綴，表示類型。有些字面值有很多類型，由VS編譯時根據上下文確定。
| TYPE(S) | CATEGORY | SUFFIX | EXAMPLE/ALLOWED VALUES |
| bool | Boolean | None | True or false |
| int, uint, long, ulong | Integer | None | 100 |
| uint, ulong | Integer | u or U | 100U |
| long, ulong | Integer | l or L | 100L |
| ulong | Integer | ul, uL, Ul, UL, lu, lU, Lu, or LU |
100UL |
| float | Real | f or F | 1.5F |
| double | Real | None, d, or D | 1.5 |
| decimal | Real | m or M | 1.5M |
| char | Character | None | 'a', or escape sequence |
| string | String | None | "a…a", may include escape sequences |
➤ 字符串轉義
所謂轉義，是將有可能破環字符串完整性的符號轉換為字符。
字符串是引用類型。可使用轉義序列、雙引號賦值。也可以被賦予null值。
| ESCAPE SEQUENCE 轉義序列 |
CHARACTER PRODUCED | UNICODE VALUE OF CHARACTER 字符的Unicode值 |
| \' | Single quotation mark 單引號 | 0x0027 |
| \" | Double quotation mark雙引號 | 0x0022 |
| \\ | Backslash反斜杠 | 0x005C |
| \0 | Null空 | 0x0000 |
| \a | Alert (causes a beep)警告（發出一個蜂鳴） | 0x0007 |
| \b | Backspace退格 | 0x0008 |
| \f | Form feed換頁 | 0x000C |
| \n | New line換行 | 0x000A |
| \r | Carriage return回車 | 0x000D |
| \t | Horizontal tab 水平制表符 | 0x0009 |
| \v | Vertical tab垂直制表符 | 0x000B |
字符串轉義舉例：
下列字符串等意：目的是把單引號看作字符串的一個字符
"Karli\'s string." "Karli\u0027s string."
使用@符號，可以不使用“轉義序列”：
@"Verbatim string literal."
上例避免某位小數點的影響。下例必須使用@
@"A short list: item 1 item 2"
下列字符串等意：
"C:\\Temp\\MyDir\\MyFile.doc" @"C:\Temp\MyDir\MyFile.doc"
3.3 運算符
➤ 簡單數學運算符
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| + | Binary | var1 = var2 + var3; | var1 is assigned the value that is the sum of var2 and var3. |
| - | Binary | var1 = var2 - var3; | var1 is assigned the value that is the value of var3 subtracted from the value of var2. |
| * | Binary | var1 = var2 * var3; | var1 is assigned the value that is the product of var2 and var3. |
| / | Binary | var1 = var2 / var3; | var1 is assigned the value that is the result of dividing var2 by var3. |
| % | Binary | var1 = var2 % var3; | var1 is assigned the value that is the remainder when var2 is divided by var3. |
| + | Unary | var1 = +var2; | var1 is assigned the value of var2. |
| - | Unary | var1 = -var2; | var1 is assigned the value of var2 multiplied by -1. |
➤ char類型和string類型運算符
注意，char類型變量的操作數不能使用上表的簡單數學運算符，否則得到的結果是一個數值。
上述+可用於string類型的操作數（如下表）。而其它運算符不能用於字符串類型的操作數。
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| + | Binary | var1 = var2 + var3; | var1 is assigned the value that is the concatenation of the two strings stored in var2 and var3. |
➤ 加/減運算符
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| ++ | Unary | var1 = ++var2; | var1 is assigned the value of var2 + 1. var2 is incremented by 1. |
| -- | Unary | var1 = --var2; | var1 is assigned the value of var2 - 1. var2 is decremented by 1. |
| ++ | Unary | var1 = var2++; | var1 is assigned the value of var2. var2 is incremented by 1. |
| -- | Unary | var1 = var2--; | var1 is assigned the value of var2. var2 is decremented by 1. |
操作數var2總是加1或減1。符號在前，結果等於操作數加1或減1。符號在后，結果等於操作數。
➤ 賦值運算符
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| = | Binary | var1 = var2; | var1 is assigned the value of var2. |
| += | Binary | var1 += var2; | var1 is assigned the value that is the sum of var1 and var2. |
| -= | Binary | var1 -= var2; | var1 is assigned the value that is the value of var2 subtracted from the value of var1. |
| *= | Binary | var1 *= var2; | var1 is assigned the value that is the product of var1 and var2. |
| /= | Binary | var1 /= var2; | var1 is assigned the value that is the result of dividing var1 by var2. |
| %= | Binary | var1 %= var2; | var1 is assigned the value that is the remainder when var1 is divided by var2. |
注意：與+一樣，+=也可以用於字符串類型的操作數。
➤ 布爾比較運算符
| OPERATOR | CATEGORY | EXPRESSION | RESULT |
| == | Binary | var1 = var2 == var3; | var1 is assigned the value true if var2 is equal to var3, or false otherwise. |
| != | Binary | var1 = var2 != var3; | var1 is assigned the value true if var2 is not equal to var3, or false otherwise. |
| < | Binary | var1 = var2 < var3; | var1 is assigned the value true if var2 is less than var3, or false otherwise. |
| > | Binary | var1 = var2 > var3; | var1 is assigned the value true if var2 is greater than var3, or false otherwise. |
| <= | Binary | var1 = var2 <= var3; | var1 is assigned the value true if var2 is less than or equal to var3, or false otherwise. |
| >= | Binary | var1 = var2 >= var3; | var1 is assigned the value true if var2 is greater than or equal to var3,or false otherwise. |
➤ 布爾值運算符
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| ! | Unary | var1 = !var2; | var1 is assigned the value true if var2 is false, or false if var2 is true. (Logical NOT) |
| & | Binary | var1 = var2 & var3; | var1 is assigned the value true if var2 and var3 are both true, or false otherwise.(Logical AND) |
| | | Binary | var1 = var2 | var3; | var1 is assigned the value true if either var2 or var3 (or both) is true,or false otherwise.(Logical OR) |
| ∧ | Binary | var1 = var2 ∧ var3; | var1 is assigned the value true if either var2 or var3, but not both, is true, or false otherwise. (Logical XOR or exclusive OR) |
➤ 條件布爾運算符
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| && | Binary | var1 = var2 && var3; | var1 is assigned the value true if var2 and var3 are both true, or false otherwise.(Logical AND) |
| || | Binary | var1 = var2 || var3; | var1 is assigned the value true if either var2 or var3 (or both) is true, or false otherwise. (Logical OR) |
➤ 布爾賦值運算符
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| &= | Binary | var1 &= var2; | var1 is assigned the value that is the result of var1 & var2. |
| |= | Binary | var1 |= var2; | var1 is assigned the value that is the result of var1 | var2. |
| ^= | Binary | var1 ^= var2; | var1 is assigned the value that is the result of var1 ^ var2. |
These work with both Boolean and numeric values in the same way as &, |, and ^.
➤ 按位運算符
| OPERAND 1 BIT | OPERAND 2 BIT | & RESULT BIT |
| 1 | 1 | 1 |
| 1 | 0 | 0 |
| 0 | 1 | 0 |
| 0 | 0 | 0 |
| OPERAND 1 BIT | OPERAND 2 BIT | & RESULT BIT |
| 1 | 1 | 1 |
| 1 | 0 | 1 |
| 0 | 1 | 1 |
| 0 | 0 | 0 |
| OPERAND 1 BIT | OPERAND 2 BIT | & RESULT BIT |
| 1 | 1 | 0 |
| 1 | 0 | 1 |
| 0 | 1 | 1 |
| 0 | 0 | 0 |
| OPERAND BIT | ~ RESULT BIT |
| 1 | 0 |
| 0 | 1 |
C# also allows the use of a unary bitwise operator (~), which acts on its operand by inverting each of its bits,so that the result is a variable having values of 1 for each bit in the operand that is 0, and vice versa. This is shown in Table 4-8.
➤ 移位運算符
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| >> | Binary | var1 = var2 >> var3; | var1 is assigned the value obtained when the binary content of var2 is shifted var3 bits to the right. |
| << | Binary | var1 = var2 << var3; | var1 is assigned the value obtained when the binary content of var2 is shifted var3 bits to the left. |
➤ 移位賦值運算符
| OPERATOR | CATEGORY | EXAMPLE EXPRESSION | RESULT |
| >>= | Unary | var1 >>= var2; | var1 is assigned the value obtained when the binary content of var1 is shifted var2 bits to the right. |
| <<= | Unary | var1 <<= var2; | var1 is assigned the value obtained when the binary content of var1 is shifted var2 bits to the left. |
3.4 運算符優先級
| PRECEDENCE | OPERATORS |
| Highest | ++, −− (used as prefi xes); (), +, – (unary), !, ˜ |
| Lowest | ++, –– (used as suffi xes) |
3.5 數據類型轉換（顯式轉換）
語法：
(<destinationType>)<sourceVar>
舉例：
byte destinationVar; short sourceVar = 7; destinationVar = (byte)sourceVar; Console.WriteLine("sourceVar val: {0}", sourceVar); Console.WriteLine("destinationVar val: {0}", destinationVar);
➤ 使用Convert 命令
| COMMAND | RESULT |
| Convert.ToBoolean(val) | val converted to bool |
| Convert.ToByte(val) | val converted to byte |
| Convert.ToChar(val) | val converted to char |
| Convert.ToDecimal(val) | val converted to decimal |
| Convert.ToDouble(val) | val converted to double |
| Convert.ToInt16(val) | val converted to short |
| Convert.ToInt32(val) | val converted to int |
| Convert.ToInt64(val) | val converted to long |
| Convert.ToSByte(val) | val converted to sbyte |
| Convert.ToSingle(val) | val converted to float |
| Convert.ToString(val) | val converted to string |
| Convert.ToUInt16(val) | val converted to ushort |
| Convert.ToUInt32(val) | val converted to uint |
| Convert.ToUInt64(val) | val converted to ulong |
Here, val can be most types of variable (if it’s a type that can’t be handled by these commands, the compiler will tell you).
4 、分支和跳轉語句
4.1 跳轉語句
➤goto 語句
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);
4.2 分支語句
➤ The ternary operator 三元運算符
➤ The if statement if語句
➤ The switch statement switch語句
4.2.1 三元運算符
常用於簡單賦值，較復雜的代碼宜用if語句。
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，則：resultString = "Less than 10"
如果myInteger≥10，則：resultString = "Greater than or equal to 10"
4.2.2 if語句
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>; }
舉例：
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(); }
舉例：判斷更多的條件：
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. } } }
4.2.3 switch語句
標准語法：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; }
5、循環語句
➤ do循環
語法：
do { <code to be looped> } while (<Test>);
舉例：
int i = 1; do { Console.WriteLine("{0}", i++); } while (i <= 10);
➤ while循環
語法：
while (<Test>) { <code to be looped> }
舉例
int i = 1; while (i <= 10) { Console.WriteLine("{0}", i++); }
➤ for循環
語法：
for (<initialization>; <condition>; <operation>) { <code to loop> }
舉例：
int i; for (i = 1; i <= 10; ++i) { Console.WriteLine("{0}", i); }
➤ 循環的中斷語句
➤ 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
➤ 無限循環
舉例：
while (true) { // code in loop }
6、高級語句
➤ 用戶輸入語句
語法：
Console.ReadLine()
➤ 類型轉換語句