// it's close!
func replaceVowels(string: String, character: String) -> String {
    var emptyString = ""
    let vowels = ["a", "e", "i", "o", "u"]

    for vowel in vowels {

        if string.contains(vowel) {
            let letter = string.replacingOccurrences(of: vowel, with: character)
            emptyString.append(letter)
        }
    }
    return emptyString
}

print(replaceVowels(string: "the aardvark", character: "?"))