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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
Updated on: 20-Jun-2020
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