swift Caesar cipher

import Foundation
/*
    Encryption Function:
    Takes a key and mutates any alphabetical character by it.

    Note: lines 29 and 32 hopefully can be trimmed
*/
func encrypt(key: Int, phrase: String) -> String {

    let key = key % 26 // very important to get key within 0-25 range!
    var arr = [Character]() // make an Array ("collection") to store encryped result phrase

    for character in phrase.unicodeScalars { // iterate throught each UnicodeScalar in phrase
        if character.value >= 65 && character.value <= 90 { // check if capital Alpha
            // append to arr: get the UnicodeScalar of the current character + key + 7 (for some reason)
            // mod it by 26 to get it within Alpha range, add 65 to get it to ASCII Alpha range
            arr.append(Character(UnicodeScalar(((Int(character.value) + key + 7) % 26) + 65)))
        } else if character.value >= 97 && character.value <= 122 { // check if lower Alpha
            // see ln25-26; same except for the lower case
            arr.append(Character(UnicodeScalar(((Int(character.value) + key + 7) % 26) + 97)))
        } else {
            // just append the original if it isn't alphabetical
            arr.append(Character(character))
        }
    }

    // return a String composed of the array from ln21
    return String(arr)
}
/*

    Decryption Function:
    Simply calls encrypt(...) with a negated key.
*/
func decrypt(key: Int, phrase: String) -> String {
    return encrypt(-key, phrase: phrase)
}
/*
    "main()"
    The controller for the program.
*/
if Process.arguments.count != 2 {
    // ln 57-60: check for correct number of arguments
    print("\nWrong number of arguments.")
    print("Usuage: caesar <key>")
} else {
    print("Put in the phrase to encrypt: ") // prompt for input, duh
    if let input = readLine() { // will exit if getting a string fails
        if let key = Int(Process.arguments[1]) { // assigns the key, exits if fails
            // ln67-71: presents user with the results
            print("Encrypting...")
            print(encrypt(key, phrase: input))

            print("Decrypting...")
            print(decrypt(key, phrase: encrypt(key, phrase: input)))
        } // curly brace
    } // another curly
} // i'm just trolling