C# 备忘清单

class Hello {
  // main method
  static void Main(string[] args)
  {
    // 输出: Hello, world!
    Console.WriteLine("Hello, world!");
  }
}

编译运行（确保在项目目录下）

$ dotnet run
Hello, world!

int intNum = 9;
long longNum = 9999999;
float floatNum = 9.99F;
double doubleNum = 99.999;
decimal decimalNum = 99.9999M;
char letter = 'D';
bool @bool = true;
string site = "jaywcjlove.github.io";
var num = 999;
var str = "999";
var bo = false;

数据类型	尺寸	范围
int	4 bytes	-2^31^ ^to^ 2^31^-1
long	8 bytes	-2^63^ ^to^ 2^63^-1
float	4 bytes	6 ^to^ 7 decimal digits
double	8 bytes	15 decimal digits
decimal	16 bytes	28 ^to^ 29 decimal digits
char	2 bytes	0 ^to^ 65535
bool	1 bit	true / false
string	2 bytes per char	N/A

// 单行注释
/* 多行
   注释 */
// TODO：向 Visual Studio 中的任务列表添加注释
/// 用于文档的单行注释
/** 多行 注释 
    用于文档 **/

string first = "John";
string last = "Doe";
// 字符串连接
string name = first + " " + last;
Console.WriteLine(name); // => John Doe

查看: C#字符串

Console.WriteLine("Enter number:");
if(int.TryParse(Console.ReadLine(),out int input))
{
  // 输入验证
  Console.WriteLine($"You entered {input}");
}

int j = 10;
if (j == 10) {
  Console.WriteLine("I get printed");
} else if (j > 10) {
  Console.WriteLine("I don't");
} else {
  Console.WriteLine("I also don't");
}

char[] chars = new char[10];
chars[0] = 'a';
chars[1] = 'b';
string[] letters = {"A", "B", "C"};
int[] mylist = {100, 200};
bool[] answers = {true, false};

int[] numbers = {1, 2, 3, 4, 5};
for(int i = 0; i < numbers.Length; i++) {
  Console.WriteLine(numbers[i]);
}

---

foreach(int num in numbers) {
  Console.WriteLine(num);
}

string first = "John";
string last = "Doe";
string name = first + " " + last;
Console.WriteLine(name); // => John Doe

string first = "John";
string last = "Doe";
string name = $"{first} {last}";
Console.WriteLine(name); // => John Doe

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.";

// 使用 System.String 的属性
string lengthOfString = "How long?";
lengthOfString.Length           // => 9
// 使用 System.String 的方法
lengthOfString.Contains("How"); // => true

var sb = new StringBuilder();
for (int i = 0; i < 100; i++)
{
    sb.Append(i.ToString());
}
Console.WriteLine(sb.ToString());
// => 123456789....

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