Compiler Error CS0023

Operator 'operator' cannot be applied to operand of type 'type'

An attempt was made to apply an operator to a variable whose type was not designed to work with the operator. For more information, see Types and C# Operators.

The following sample generates CS0023:

// CS0023.cs  
namespace x  
{  
   public class a  
   {  
      public static void Main()  
      {  
         string s = "hello";  
         s = -s;   // CS0023, minus operator not allowed on strings  
      }  
   }  
}