Every year, CS50 changes what `check50` is looking for. You are using the 2016 version - you need to change to what the 2017 `check50` is looking for, which is this:

    ~/workspace/pset2/ $ ./caesar 12
    plaintext: world, say hello!
    ciphertext: iadxp, emk tqxxa!

Can you see the added `plaintext:` and `ciphertext:`? To see the 2017 instructions, go [here][1]. Basically, you need to make sure that you are following the *new* CS50 instructions.


  [1]: http://docs.cs50.net/2017/x/psets/2/pset2.html