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What are C# pre-processor directives?
The preprocessor directives give instruction to the compiler to preprocess the information before actual compilation starts.
All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Preprocessor directives are not statements, so they do not end with a semicolon (;).
The following are some of the preprocessor directives in C#.
Sr.No | Preprocessor Directive & Description |
---|---|
1 | #define It defines a sequence of characters, called symbol. |
2 | #undef It allows you to undefine a symbol. |
3 | #if It allows testing a symbol or symbols to see if they evaluate to true. |
4 | #else It allows to create a compound conditional directive, along with #if. |
5 | #elif It allows creating a compound conditional directive. |
6 | #endif Specifies the end of a conditional directive. |
7 | #line It lets you modify the compiler's line number and (optionally) the file name output for errors and warnings. |
8 | #error It allows generating an error from a specific location in your code. |
Let us see an example of the #define preprocessor that defines a sequence of characters.
Example
#define PI using System; namespace PreprocessorDAppl { class Program { static void Main(string[] args) { #if (PI) Console.WriteLine("PI is defined"); #else Console.WriteLine("PI is not defined"); #endif Console.ReadKey(); } } }
Output
PI is defined
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