func numberOfVowels(in string: String) -> String {
    var count = 0
    for vowels in string.lowercased() {
        switch vowels {
        case "a", "e", "i", "o", "u":
            print(vowels)
            count += 1
        default:
            break
        }
    }
    return "There are \(count) vowels in \"\(string)\""
}
numberOfVowels(in: "Hello World")