Csharp

net 框架

dotnet --version # 版本信息
dotnet new console -o <project-name> # 创建一个新的控制台应用
dotnet run # 编译并运行一个C#程序

数据类型

值类型：基本类型（字符串除外），枚举，元组和结构
引用类型：类，字符串，接口，数组和委托

字符串

字符串可变性

• System.String：不可变的字符序列
• System.Text.StringBuilder：变的字符序列 ```csharp using System; char[] cdb = { ‘M’, ‘y’, ‘S’, ‘q’, ‘l’ }; string db = new string(cdb); // MySql

string lang = “C#”; // C# String ide = “NetBeans”; // NetBeans

```csharp
using System.Text;
string lang = "C#";
StringBuilder sb1 = new StringBuilder(lang); // C#
StringBuilder sb2 = new StringBuilder(); // Fields of glory
sb2.Append("Fields");
sb2.Append(" of ");
sb2.Append("glory");
sb.Remove(sb.Length-1, 1);
sb.Insert(3, ' ');
sb.Replace('M', 'm', 4, 1);

字符串是对象

对象必须具有一个类名，一个父类，并且还必须具有可以调用的方法或要访问的属性。

using System;
string lang = "Java";
string bclass = lang.GetType().Name; // String
string parclass = lang.GetType().BaseType.Name; // Object
var isEmpty = lang.Equals(String.Empty); // false
int len = lang.Length; // 4

连接字符串

"Return" + " of " + "the king.";
string.Concat(string.Concat("Return", " of ");
StringBuilder sb = new StringBuilder();
sb.Append("Return");
sb.Append(" of ");
sb.Append("the king."); 
var items = new string[] { "C#", "Visual Basic", "Java", "Perl" };
string langs = string.Join(",", items); // C#,Visual Basic,Java,Perl
string[] langs2 = langs.Split(','); // [C#,Visual Basic,Java,Perl]

转义

using System;
string s1 = "deep \t forest"; // deep     forest

不转义

using System;
Console.WriteLine(@"deep \t forest"); // deep \t forest

字符串格式化string.Format

using System;
int age = 34;
string name = "William";
string msg = string.Format("{0} is {1} years old.", name, age); // William is 34 years old.

字符串插值$

using System;
string name = "Peter";
int age = 34;
string msg = $"{name} is {age} years old"; // Peter is 34 years old

常用方法

using System;
string word = "Determination";
Console.WriteLine(word.Contains("e")); // 包含特定字符
Console.WriteLine(word.IndexOf("e")); // 返回字符串中字母的第一个索引
Console.WriteLine(word.LastIndexOf("i")); // 返回字符串中字母的最后一个索引
Console.WriteLine(word.ToUpper()); // 转换为大写
Console.WriteLine(word.ToLower()); // 转换为小写
string cloned = (string) str.Clone(); // ReferenceEquals(str, cloned) = true
string copied = string.Copy(str); // ReferenceEquals(str, cloned) = false

数组

int[] array = new int[] {2, 4, 5, 6, 7, 3, 2 }; // 初始化
int[] vals2 = vals[1..5]; // 数组切片，[4, 5, 6, 7, 3]
int[] vals3 = vals[..6]; // [2, 4, 5, 6, 7, 3, 2 ]
int[] vals4 = vals[3..]; // [6, 7, 3, 2]
for (int i=0; i < array.Length; i++) {} // 数组遍历
foreach (string planet in array) {}
names.GetValue(1);
names.SetValue("Beky", 1);
Array.Sort(names); 
Array.Reverse(names);
Array.IndexOf(names, "Erzebeth");
Array.Copy(names, girls, names.Length);
Array.Clear(names, 0, 2);

字符

using System;
string word = "ZetCode";
char c = word[0]; // Z

元组

using System;
var words = ("sky", "blue", "rock", "fountain");
Console.WriteLine(words.Item1); // sky
Console.WriteLine(words.Item2); // blue

DateTime

using System;
DateTime now = DateTime.Now; // 12/5/2018 8:09:56 PM
DateTime now1 = DateTime.Now.ToShortDateString(); // 12/5/2018
DateTime now2 = DateTime.Now.ToShortTimeString(); // 8:09 PM

可空类型?

using System;
Nullable<bool> male = null;
int? age = null;

类型转换（）

using System;
double b = 13.5;
float a = (float) b; // 将double值转换为float值

值转换Convert

using System;
// 将double值转换为bool值
Console.WriteLine(Convert.ToBoolean(0.3));
Console.WriteLine(Convert.ToBoolean(3));
Console.WriteLine(Convert.ToBoolean(0));
Console.WriteLine(Convert.ToBoolean(-1));
Console.WriteLine(Convert.ToInt32("452"));
Console.WriteLine(Convert.ToInt32(34.5));
// 将string转换为int值
Console.WriteLine(Int32.Parse("34"));
Console.WriteLine(Int32.Parse("-34"));
Console.WriteLine(Int32.Parse("+34"));

C# 运算符

控制台的值Console.ReadLine

using System;
Console.WriteLine("This is C#"); // 等同于System.Console.WriteLine("This is C#");
string name = Console.ReadLine(); // 从控制台读取一个值

数组定义List

using System.Collections.Generic;
var words = new List<string> { "stone", "rock", "falcon", "sky" };

解构丢弃_

using System;
var vals = (1, 2, 3, 4, 5, 6);
(int x, int y, int z, _, _, _) = vals;

生成指定范围内的数字序列Enumerable.Range

using System.Linq;
var vals = Enumerable.Range(1, 6); // [1,2,3,4,5,6]

随机数random

using System;
Random random = new Random();