iOS - 字符串操作for遍历

使用for循环遍历字符串，并获取字符，包含正序遍历字符串，逆序遍历字符串

let string:String = "Hello, playground"/// 正序遍历字符串for i in 0 ..< string.characters.count {    let c = (str as NSString).characterAtIndex(i)    let cStr = Character(UnicodeScalar(c))    print(cStr)}/// 逆序遍历字符串let startIndex = string.characters.count - 1for i in startIndex.stride(to: -1, by: -1) {    let c = (str as NSString).characterAtIndex(i)    let cStr = Character(UnicodeScalar(c))    print(cStr)}