As OriginalGriff has said your search code looks fine to me.
The results you are getting do not make sense though as whatever number you search for should come up as NOT found.
In your calling code you assign
a
the value -1, but thereafter it is not changed. So a small change should cure this:
int a = bs.Binary(unsorted, searchvalue);
if (a == -1)
Console.Out.WriteLine("Element " + searchvalue + " was not found!");
else
Console.Out.WriteLine("Element " + searchvalue + " was found.");