How to Define Constants in Visual C# Like #Define in C?

You can't do this in C#. Use a const int instead.

static class Constants
{
    public const int MIN_LENGTH = 5;
    public const int MIN_WIDTH  = 5; 
    public const int MIN_HEIGHT = 6;
}

// elsewhere
public CBox()
{
    length = Constants.MIN_LENGTH; 
    width  = Constants.MIN_WIDTH; 
    height = Constants.MIN_HEIGHT;  
}

Check How to: Define Constants in C# on MSDN:

In C# the #define preprocessor directive cannot be used to define constants in the way that is typically used in C and C++.

in c language: #define (e.g. #define counter 100)

in assembly language: equ (e.g. counter equ 100)

in c# language: according to msdn refrence: You use #define to define a symbol. When you use the symbol as the expression that's passed to the #if directive, the expression will evaluate to true, as the following example shows:

# define DEBUG

The #define directive cannot be used to declare constant values as is typically done in C and C++. Constants in C# are best defined as static members of a class or struct. If you have several such constants, consider creating a separate "Constants" class to hold them.

In C#, per MSDN library, we have the "const" keyword that does the work of the "#define" keyword in other languages.

"...when the compiler encounters a constant identifier in C# source code (for example, months), it substitutes the literal value directly into the intermediate language (IL) code that it produces." ( )

Initialize constants at time of declaration since there is no changing them.

public const int cMonths = 12;

What is the "Visual C#"? There is no such thing. Just C#, or .NET C# :)

Also, Python's convention for constants CONSTANT_NAME is not very common in C#. We are usually using CamelCase according to MSDN standards, e.g. public const string ExtractedMagicString = "vs2019";

Source: Defining constants in C#