Compiler Error CS1025

Single-line comment or end-of-line expected

A line with a preprocessor directive cannot have a multiline comment.

The following sample generates CS1025:

#if true /* hello  
*/   // CS1025  
#endif   // this is a good comment  

CS1025 could also occur if you attempt some invalid preprocessor directive, as follows:

// CS1025.cs  
#define a  
  
class Sample  
{  
   static void Main()  
   {  
      #if a 1   // CS1025, invalid syntax  
         System.Console.WriteLine("Hello, World!");  
      #endif  
   }  
}