Is the use of Struct or Class personal preference?
This MSDN Page states:


  CONSIDER defining a struct instead of a class
  
  
  if instances of the type are small and commonly short-lived or are commonly embedded in other objects.
  
  
  AVOID defining a struct unless the type has all of the following characteristics:
  
  
  It logically represents a single value, similar to primitive types (int, double, etc.).  
  It has an instance size under 16 bytes.  
  It is immutable.  
  It will not have to be boxed frequently.  
  


So if you want to use a class instead of a structure, you can just add the same static goofy method, to get the same style like you get with the structure:  

   public static retclass goofie(int isn, string ss)
    {
        retclass dex = new retclass();
        dex.str = ss;
        dex.num = isn;
        if ((dex.str != "") &amp;&amp; (dex.num &gt; 0))
        {
            dex.yesno = true;
        }
        return dex;
    }


You can either add this to the Main or better inside the class itself. If you consider the second, you can call it like:  

retclass x = retclass.goofie(3, "this is the reclass string");

Console.WriteLine("The String is {0}, the int is {1} and the value 
      is {2}", x.str, x.num, x.yesno);