To lower case implementation in swift.

ToLowerCase.swift

func toLowerCase(string: String) -> String {
    var str = string as NSString
    for i in 0...(str.length - 1) {
        if str.character(at: i) >= 65 && str.character(at: i) <= 90 {
            let changeValue = str.character(at: i) + 32

            str = str.replacingCharacters(in: NSMakeRange(i, 1), with: String(Character(UnicodeScalar(changeValue)!))) as NSString
        }
    }
    return str as String
}

toLowerCase(string: "convErTing StrinG inTo Lower Case") //result "converting string into lower case"