There is no "else if" in DBP, you'll have to nest if-clauses within else's yourself. As such what you have there could be rewritten as
if police = 1
i = "arial"
else
if police = 2
i = "comic"
else
print "oh!!!"
endif
rem « Missing the endif keyword here, hence the "could not close nest" error
I don't know if you're new to programming but if you are I would recommend using a switch clause (which for whatever reason is called
select in DarkBASIC by the way) for the kind of thing you are doing there.
You would use it like so:
select police
case 1
i = "arial"
endcase
case 2
i = "comic"
endcase
case default
print "oh!!!" rem This case is matched if none of the others apply
endcase
endselect
"Why do programmers get Halloween and Christmas mixed up?" Because Oct(31) = Dec(25)