案例 31：LINQ 查询学生成绩排序
说明：演示如何使用 LINQ 查询并排序数据集合。
using System;
using System.Collections.Generic;
using System.Linq;
class Program
{
class Student
{
public string Name { get; set; }
public int Score { get; set; }
}
static void Main()
{
var students = new List<Student>
{
new Student { Name = "Tom", Score = 85 },
new Student { Name = "Jerry", Score = 92 },
new Student { Name = "Lucy", Score = 78 }
};
var result = students.OrderByDescending(s => s.Score);
foreach (var student in result)
{
Console.WriteLine(#34;{student.Name}: {student.Score}");
}
}
}
输出：
Jerry: 92
Tom: 85
Lucy: 78
案例 32：序列化与反序列化 JSON（使用 System.Text.Json）
using System;
using System.Text.Json;
class Program
{
class User
{
public string Name { get; set; }
public int Age { get; set; }
}
static void Main()
{
User user = new User { Name = "Alice", Age = 28 };
string json = JsonSerializer.Serialize(user);
Console.WriteLine("Serialized: " + json);
User deserialized = JsonSerializer.Deserialize<User>(json);
Console.WriteLine("Deserialized: " + deserialized.Name + ", " + deserialized.Age);
}
}
输出：
Serialized: {"Name":"Alice","Age":28}
Deserialized: Alice, 28
案例 33：反转字符串
using System;
class Program
{
static void Main()
{
string input = "Hello World";
char[] chars = input.ToCharArray();
Array.Reverse(chars);
string reversed = new string(chars);
Console.WriteLine(reversed);
}
}
输出：
dlroW olleH
案例 34：创建自定义异常
using System;
class MyException : Exception
{
public MyException(string message) : base(message) { }
}
class Program
{
static void Main()
{
try
{
throw new MyException("这是自定义异常！");
}
catch (MyException ex)
{
Console.WriteLine("捕获异常: " + ex.Message);
}
}
}
输出：
捕获异常: 这是自定义异常！
案例 35：简单计算器（加减乘除）
using System;
class Program
{
static void Main()
{
double a = 10, b = 5;
Console.WriteLine(#34;加法: {a + b}");
Console.WriteLine(#34;减法: {a - b}");
Console.WriteLine(#34;乘法: {a * b}");
Console.WriteLine(#34;除法: {a / b}");
}
}
输出：
加法: 15
减法: 5
乘法: 50
除法: 2
案例 36：列出文件夹下所有文件（使用 System.IO）
using System;
using System.IO;
class Program
{
static void Main()
{
string[] files = Directory.GetFiles(@"C:\Windows");
foreach (string file in files)
{
Console.WriteLine(file);
}
}
}
输出：（示例）
C:\Windows\explorer.exe
C:\Windows\notepad.exe
...
案例 37：使用 Thread 创建线程
using System;
using System.Threading;
class Program
{
static void Print()
{
Console.WriteLine("子线程运行中...");
}
static void Main()
{
Thread t = new Thread(Print);
t.Start();
Console.WriteLine("主线程结束");
}
}
输出：
主线程结束
子线程运行中...
案例 38：使用 lock 实现线程同步
using System;
using System.Threading;
class Program
{
static int count = 0;
static object locker = new object();
static void Add()
{
for (int i = 0; i < 1000; i++)
{
lock (locker)
{
count++;
}
}
}
static void Main()
{
Thread t1 = new Thread(Add);
Thread t2 = new Thread(Add);
t1.Start(); t2.Start();
t1.Join(); t2.Join();
Console.WriteLine("Count = " + count);
}
}
输出：
Count = 2000
案例 39：Web 请求示例（使用 HttpClient）
using System;
using System.Net.Http;
using System.Threading.Tasks;
class Program
{
static async Task Main()
{
HttpClient client = new HttpClient();
string html = await client.GetStringAsync("https://example.com");
Console.WriteLine(html.Substring(0, 100)); // 截取前100字符
}
}
输出：（示例）
<!doctype html>
<html>
<head>
<title>Example Domain</title>
...
案例 40：读取并写入文本文件
using System;
using System.IO;
class Program
{
static void Main()
{
string path = "test.txt";
File.WriteAllText(path, "Hello, file!");
string content = File.ReadAllText(path);
Console.WriteLine(content);
}
}
输出：
Hello, file!