Compiler Error CS1020

Overloadable binary operator expected

An attempt was made to define an operator overload, but the operator was not a binary operator, which takes two parameters.

The following sample generates CS1020:

// CS1020.cs
public class iii
{
   public static int operator ++(iii aa, int bb)   // CS1020, change ++ to +
   {
      return 0;
   }

   public static void Main()
   {
   }
}