C# program basic structure and commonly used variables C# learning miscellaneous notes (1)

1. Basic structure of C# program The
first step is to create a new C# project


VS will automatically generate some basic code

using System;//引用命名空间

namespace boke_01//定义命名空间
{
    
    
    class Program//定义类
    {
    
    
        static void Main(string[] args)//定义方法，这里是创建项目时自动创建好的主程序方法
        {
    
    
            //程序的入口点
        }
    }
}

First understand the Main function. It is the entry point of the program. Under normal circumstances, a project can only have one Main function, otherwise it will fail to compile, and the Main function must be static (with static keyword)
C# input and output method

static void Main(string[] args)
        {
    
    
            //输出
            Console.WriteLine("hello C# !");

            //输入
            //Console.ReadLine会返回string类型，一般会声明一个string类型变量来接收
            string input = Console.ReadLine();
        }

2. C# commonly used variable types
(1) Value types (Value types)
Value type variables can be directly assigned to a value. They are derived from the class System.ValueType.

	bool boke;//bool值，值为true或者false，默认为false
    char s = 'a';//字符类型
    int num = 2;//32位，整数类型
    long num1 = 2;//64位，整数类型
    float number = 2.3f;//单精度浮点型，f 表示float类型
    double number1 = 4.6d;//双精度浮点型，d 表示double类型
    byte byte_b = 2;//byte类型，0-255，此语句中其实是将整数 1 隐式转换为byte类型

(2) Reference types Reference types
do not contain actual data stored in variables, they refer to a memory location. When using multiple variables, the reference type can point to a memory location. If the data in the memory location is changed by a variable, other variables will automatically reflect this change in value. The built-in reference types are: object, dynamic and string.
[1] Object type·
In C#, Object type is the root of all types, and Object data type can point to data of any data type

		object obj = "cxk";
        object obj1 = 123;

But note: when a value type is converted to an object type, it is called boxing; on the other hand, when an object type is converted to a value type, it is called unboxing.
Although the Object type is more convenient to use, the unpacking and unpacking operations consume performance and depend on the situation.
[2] Dynamic (Dynamic) type
can store any type of value in a variable of dynamic data type. The type checking of these variables occurs at runtime.

dynamic dy = "dsfsd";//动态类型

The most commonly used dynamic type is to always store json data.
[3] String type

	string str = "lay";//字符串类型

    //表示路径的时候，前面加@，将‘/’当成普通字符处理，否则可能会识别为转义符
    string path = @"C:\Users\Public\Desktop\腾讯QQ.lnk";

[4] Pointer type
When a code block is marked with the unsafe modifier, C# allows pointer variables to be used in the function.
But this is unsafe code.

       static unsafe void Main(string[] args)
        {
    
    
            int p1 = 20;
            int* p = &p1;//将地址赋给指针
        }

  static void Main(string[] args)
        {
    
    
            unsafe
            {
    
    
                int p1 = 20;
                int* p = &p1;//将地址赋给指针
            }
        }

It should be noted that C# is a strictly case-sensitive language.