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How to use #if..#elif…#else…#endif directives in C#?
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 (;).
#if
The #if directive allows testing a symbol or symbols to see if they evaluate to true.
#else
It allows to create a compound conditional directive, along with #if.
#elif
It allows creating a compound conditional directive.
#endif
The #endif specifies the end of a conditional directive.
The following is an example showing the usage of #if, #elif, #else and #endif directives −
Example
#define One #undef Two using System; namespace Demo { class Program { static void Main(string[] args) { #if (One && TWO) Console.WriteLine("Both are defined"); #elif (ONE && !TWO) Console.WriteLine("ONE is defined and TWO is undefined"); #elif (!ONE && TWO) Console.WriteLine("ONE is defined and TWO is undefined"); #else Console.WriteLine("Both are undefined"); #endif } } }
Output
Both are undefined
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