decl string mode
while (not (or (= mode "encode") (= mode "decode")))
	out "encode/decode: " console
	set mode (lower (in string console))
end while

decl string message
out "message:       " console
set message (upper (in string console))

decl int key
out "key:           " console
set key (in int console)
if (or (> key 26) (< key 0))
	out endl "invalid key" endl console
	stop
end if

if (= mode "decode")
	set key (int (- 26 key))
end if

for (decl int i) (< i (size message)) (inc i)
	if (and (> (ord message<i>) 64) (< (ord message<i>) 91))
		out (chr (int (+ (mod (int (+ (- (ord message<i>) 65) key)) 26) 65))) console
	end if
end for
out endl console