The program exits unexpectedly

[unDEFER via Digitalmars-d-learn]

On Friday, 9 December 2016 at 14:29:38 UTC, unDEFER wrote:
> I'm afraid that the problem that my program wants to say 
> something, but there is no "flush" so message leaves in the 
> buffer.

I have found, it was code like:

string path = "C:";
string parent = path[0..path.lastIndexOf("\\")];

And in mini program it works and shows diagnostic message.
Where my diagnostic message in more complicate program???