 newKey = (26+shift)%26
 
 var origmessage = ""
-newAlpha = letterLists.21.alphabet
+newAlpha = letterLists[newKey].alphabet
 
 for i in newMessage.uppercaseString.characters {
     switch i {

    (loc: 23, alphabet: "XYZABCDEFGHIJKLMNOPQRSTUVW"),
    (loc: 24, alphabet: "YZABCDEFGHIJKLMNOPQRSTUVWX"),
    (loc: 25, alphabet: "ZABCDEFGHIJKLMNOPQRSTUVWXY")
)

var message = "abe lincoln"
var shift = 5

var newKey = (26+shift)%26
var newAlpha = letterLists.5.alphabet
//need to substitute 'newKey' in 'newAlpha' to find the 'newKey'th

var newMessage = ""

Try using plain tuples
*/

var letterLists = [
    (loc: 0, alphabet: "ABCDEFGHIJKLMNOPQRSTUVWXYZ"),
    (loc: 1, alphabet: "BCDEFGHIJKLMNOPQRSTUVWXYZA"),
    (loc: 2, alphabet: "CDEFGHIJKLMNOPQRSTUVWXYZAB"),
