What is a pre-processor directive in C#?

C# compiler does not have a separate preprocessor; however, the directives are processed as if there was one. In C# the preprocessor directives are used to help in conditional compilation.

The preprocessor directives give instruction to the compiler to preprocess the information before actual compilation starts.

The following are the preprocessor directives in C# −

Let us see an example to learn about the usage of pre-processor directive in C# −

Example

#define PI
using System;

namespace Demo {
   class Program {
      static void Main(string[] args) {
         #if (PI)
         Console.WriteLine("PI is defined");
         #else
         Console.WriteLine("PI is not defined");
         #endif
         Console.ReadKey();
      }
   }
}