Program:

The source code to demonstrate the #if preprocessor directive is given below. The given program is compiled and executed successfully on Microsoft Visual Studio.

//C# program to demonstrate the
//#if preprocessor directive.

#define MY_MACRO
using System;
using System.Diagnostics;

class Program
{
   public static void Main()
    {
        #if (MY_MACRO)
            Console.WriteLine("Macro is defined");
        #else
            Console.WriteLine("Macro is not defined");
        #endif
    }
}

Output:

Macro is defined
Press any key to continue . . .

Explanation:

In the above program, we defined a macro "MY_MACRO". Here we created a class Program that contains the Main() method. The Main() method is the entry point for the program. Here, we checked "MY_MACRO" is defined or not. In our program, we already defined the "MY_MACRO" that's why the "Macro is defined" message will be printed on the console screen.