That's strange, because your first problem doesn't create any problems this end:
dim stack$(10) : stack$(1) = "test"
dim new_speed#(10) : new_speed#(1) = 10
choice = 1
cli$ = right$(stack$(choice),5) + ", accelerate to " + str$(new_speed#(choice)) + "kts. Over."
print cli$
wait key : end
And your second problem compiles OK for me as well.
Are you using the demo of DBPro or have you not yet upgraded to patch 3.1? Either case could be significant.
Programming anything is an art, and you can't rush art.
Unless your name is Bob Ross, then you can do it in thirty minutes.