What are preprocessor directives in C#?

The C# compiler does not have a separate preprocessor; however, these directives are processed as if there were one. In C#, preprocessor directives are used to aid conditional compilation.

Preprocessor directives issue instructions to the compiler to preprocess information before actual compilation begins.

The following are the preprocessor directives in C#-

6

Sr.No.	Preprocessor Directives & Description
1	#define It defines a sequence of characters, called a symbol.
2	#undef It allows you to undefine symbols.
3	#if It allows testing one or more symbols to see them Whether the calculation result is true.
4	#else It allows creating compound conditional directives together with #if.
5	#elif It allows the creation of compound conditional instructions.
#endif Specifies the end of the conditional directive.
7	#line It allows you to modify the compiler's line numbers as well as ( Optional) Filename output for errors and warnings.
8	#error It allows generating errors coming from specific locations in the code.
9	#warning It allows to generate one level from a specific location in the code warn.
10	#region It allows you to specify when using the Visual Studio Code Editor The outline feature allows you to expand or collapse blocks of code.
11	#endregion It marks the end of the #region block.

Let’s see an example to understand the usage of preprocessor directives 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();
      }
   }
}

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