RosettaCodeData/Task/Caesar-cipher/Ursa/caesar-cipher.ursa

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