229 lines
5.2 KiB
Markdown
229 lines
5.2 KiB
Markdown
C# 备忘清单
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===
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提供基本语法和方法的 C# 快速参考备忘单
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入门
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--------
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### Hello.cs
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```cs
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class Hello {
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// main method
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static void Main(string[] args)
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{
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// 输出: Hello, world!
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Console.WriteLine("Hello, world!");
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}
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}
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```
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编译运行（确保在项目目录下）
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```shell
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$ dotnet run
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Hello, world!
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```
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### 变量
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```cs
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int intNum = 9;
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long longNum = 9999999;
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float floatNum = 9.99F;
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double doubleNum = 99.999;
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decimal decimalNum = 99.9999M;
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char letter = 'D';
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bool @bool = true;
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string site = "jaywcjlove.github.io";
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var num = 999;
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var str = "999";
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var bo = false;
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```
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### 原始数据类型
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数据类型 | 尺寸 | 范围
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:- | - | -
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| `int` | 4 bytes | -2^31^ ^to^ 2^31^-1 |
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| `long` | 8 bytes | -2^63^ ^to^ 2^63^-1 |
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| `float` | 4 bytes | 6 ^to^ 7 decimal digits |
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| `double` | 8 bytes | 15 decimal digits |
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| `decimal` | 16 bytes | 28 ^to^ 29 decimal digits |
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| `char` | 2 bytes | 0 ^to^ 65535 |
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| `bool` | 1 bit | true / false |
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| `string` | 2 bytes per char | _N/A_ |
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<!--rehype:className=show-header-->
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### 注释
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```cs
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// 单行注释
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/* 多行
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注释 */
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// TODO：向 Visual Studio 中的任务列表添加注释
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/// 用于文档的单行注释
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/** 多行 注释
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用于文档 **/
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```
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### 字符串
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```cs
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string first = "John";
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string last = "Doe";
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// 字符串连接
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string name = first + " " + last;
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Console.WriteLine(name); // => John Doe
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```
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查看: [C#字符串](#c-字符串)
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### 用户输入
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```cs showLineNumbers
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Console.WriteLine("Enter number:");
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if(int.TryParse(Console.ReadLine(),out int input))
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{
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// 输入验证
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Console.WriteLine($"You entered {input}");
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}
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```
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### 条件判断
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```cs
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int j = 10;
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if (j == 10) {
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Console.WriteLine("I get printed");
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} else if (j > 10) {
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Console.WriteLine("I don't");
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} else {
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Console.WriteLine("I also don't");
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}
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```
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### 数组
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```cs
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char[] chars = new char[10];
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chars[0] = 'a';
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chars[1] = 'b';
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string[] letters = {"A", "B", "C"};
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int[] mylist = {100, 200};
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bool[] answers = {true, false};
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```
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### 循环
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```cs
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int[] numbers = {1, 2, 3, 4, 5};
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for(int i = 0; i < numbers.Length; i++) {
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Console.WriteLine(numbers[i]);
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}
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```
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---
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```cs
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foreach(int num in numbers) {
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Console.WriteLine(num);
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}
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```
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C# 字符串
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----------------
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### 字符串连接
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```cs
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string first = "John";
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string last = "Doe";
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string name = first + " " + last;
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Console.WriteLine(name); // => John Doe
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```
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### 字符串插值
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```cs
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string first = "John";
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string last = "Doe";
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string name = $"{first} {last}";
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Console.WriteLine(name); // => John Doe
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```
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### 字符串成员
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<!--rehype:wrap-class=row-span-2-->
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成员 | 说明
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:- | -
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`Length` | 返回字符串长度的属性
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`Compare()` | 比较两个字符串的静态方法
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`Contains()` | 确定字符串是否包含特定的子字符串
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`Equals()` | 确定两个字符串是否具有相同的字符数据
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`Format()` | 通过 {0} 表示法和使用其他原语格式化字符串
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`Trim()` | 从尾随和前导字符中删除特定字符的所有实例。 默认删除前导和尾随空格
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`Split()` | 删除提供的字符并从两侧的剩余字符中创建一个数组
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<!--rehype:className=show-header-->
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### 逐字字符串
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```cs showLineNumbers
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string longString = @"I can type any characters in here !#@$%^&*()__+ '' \n \t except double quotes and I will be taken literally. I even work with multiple lines.";
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```
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<!--rehype:className=wrap-text-->
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### 成员示例
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```cs
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// 使用 System.String 的属性
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string lengthOfString = "How long?";
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lengthOfString.Length // => 9
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// 使用 System.String 的方法
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lengthOfString.Contains("How"); // => true
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```
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### 频繁字符串拼接
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```cs
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var sb = new StringBuilder();
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for (int i = 0; i < 100; i++)
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{
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sb.Append(i.ToString());
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}
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Console.WriteLine(sb.ToString());
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// => 123456789....
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```
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对于频繁拼接字符串的场景（如：成百上千次循环），使用 `System.Text.StringBuilder` 提升性能
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### 原始字符串文本
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<!--rehype:wrap-class=col-span-2-->
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```cs
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// C#11 语法, 至少3个双引号(""")开头和结尾，内容可以输入任何原始字符
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// 单行: 左引号，右引号，内容 三者同行
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string singleLine = """Content begin "Hello World!" end.""";
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// 多行：左引号，右引号各一行，内容需与右引号缩进对齐
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string multiLine = """
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Content begin "Hello World!" /\n<>"" end.
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""";
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Console.WriteLine(multiLine); // => Content begin "Hello World!" /\n<>"" end.
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```
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杂项
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-----------
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### 常用 .NET 概念
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<!--rehype:wrap-class=col-span-3-->
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概念 | 中文名 | 定义
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:- | -|--
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Runtime | 运行时 | 执行给定的已编译代码单元所需的服务集合
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Common Language Runtime (CLR) | 通用语言运行库 | 主要定位、加载和托管 .NET 对象。<br/>CLR 还处理内存管理、应用程序托管、线程协调、执行安全检查和其他低级细节
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Managed code | 托管代码 | 在 `.NET` 运行时编译和运行的代码。 C#/F#/VB 就是例子
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Unmanaged code | 非托管代码 | 直接编译为机器代码且不能由 .NET 运行时直接托管的代码。<br/>不包含空闲内存管理、垃圾收集等。从 C/C++ 创建的 DLL 就是示例
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<!--rehype:className=show-header-->
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