Perhaps the most basic description of a computer program is that it is a series of operations that manipulate data.

third type of comment in C#

/// A special comment that start with three / symbols instead of two.

You can configure Visual Studio to extract the text after these comments and create a specially formatted text file when a project is compiled.you can then use it to create documentation.

#region and #endregion keywords
How to achieve the code outlining functionality. You can do this with the #region and #endregion keywords, which define the start and end of a region of code that can be expanded and collapsed.

#region Using directives
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
#endregion
 

C# preprocessor directives

Integer Types

The names you use for these types in C# are aliases for the types defined in the framework.
Floating-Point Types

Text and Boolean Types

Note that there is no uper limit on the number of characters making up a string, because it can use varying amounts of memory.
Literal Values

digit separators

public const double Pi = 3.141_592_653_589_793_238_462_643_383_279_502;

原義字串Verbatim strings

            string location = "C:\\Temp\\MyDir\\MyFile.doc";
            // location2 和 location相同
            string location2 = @"C:\Temp\MyDir\MyFile.doc";

自增和自減運算子

int var1, var2 = 5, var3 = 6;
// var1 = 25;
var1 = var2++ * --var3;

Placing one of these operators before its operand means that the operand is affected before any other computation takes place. Placing it after the operand means that the operand is affected after all other computation of the expression is completed.

$""

double firstNumber = 5, secondNumber = 6;
// The sum of 5 and 6 is 11
Console.WriteLine($"The sum of {firstNumber} and {secondNumber} is " + $"{firstNumber + secondNumber}.");