Checks if typed in message contains a character that doesn't fit A-Z, 0-9 & _.

latin.swift

import Foundation
import UIKit

func unallowedCharacter(word: String, alert: Bool) -> AnyObject {
    
var arrayOfString = Array(word.characters)
var containsUnallowedCharacter = false

for i in 0...arrayOfString.count - 1 {
    var currentCharacter: String = String(arrayOfString[i]).lowercaseString
    if currentCharacter != "a"
        && currentCharacter != "b"
        && currentCharacter != "c"
        && currentCharacter != "d"
        && currentCharacter != "e"
        && currentCharacter != "f"
        && currentCharacter != "g"
        && currentCharacter != "h"
        && currentCharacter != "i"
        && currentCharacter != "j"
        && currentCharacter != "k"
        && currentCharacter != "l"
        && currentCharacter != "m"
        && currentCharacter != "n"
        && currentCharacter != "o"
        && currentCharacter != "p"
        && currentCharacter != "q"
        && currentCharacter != "r"
        && currentCharacter != "s"
        && currentCharacter != "t"
        && currentCharacter != "u"
        && currentCharacter != "v"
        && currentCharacter != "w"
        && currentCharacter != "x"
        && currentCharacter != "y"
        && currentCharacter != "z"
        && currentCharacter != "0"
        && currentCharacter != "1"
        && currentCharacter != "2"
        && currentCharacter != "3"
        && currentCharacter != "4"
        && currentCharacter != "5"
        && currentCharacter != "6"
        && currentCharacter != "7"
        && currentCharacter != "8"
        && currentCharacter != "9"
        && currentCharacter != "_" {
        containsUnallowedCharacter = true
        } else {
        containsUnallowedCharacter = false
        }
    }
    
    if containsUnallowedCharacter == true {
        if alert == false {
            return containsUnallowedCharacter
        } else {
            let characterAlert = UIAlertController(title: "Your username contains at least one invalid character. You are allowed to type in A-Z, 0-9 and _", message: nil, preferredStyle: .Alert)
            
            let action = UIAlertAction(title: "OK", style: .Default) {
                (action) in
                
                print("Okay")
            }
            
            characterAlert.addAction(action)
            
            return characterAlert
        }

    } else {
        return containsUnallowedCharacter
    }
    
    }

unallowedCharacter("Hezü", alert: true)