It's been a while since I've used C#, but I'd guess it's because the C++ is doing a "+=" with ",", to cram two statements in there, while C# considers "+=" a to

It's been a while since I've used C#, but I'd guess it's because the C++ is doing a "+=" with ",", to cram two statements in there, while C# considers "+=" a toplevel statement only and doesn't allow it to be used with ",".