How to use #undef directive in C#?

The #undef directive allows you to undefine a symbol. The following is the syntax −

#undef SYMBOL

For example,

#undef One

It evaluates to false when used along with #if directive. Let us see an example −

Example

 Live Demo

#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