objective-c获取字符串的最后2个字符？

Question

说我有一个字符串：

NSString *state = @"California, CA";

有人可以告诉我如何从这个字符串中提取最后两个字符（在本例中为@“CA”）

Answer 1

NSString *code = [state substringFromIndex: [state length] - 2];

应该这样做

Answer 2

Swift 4：

let code = (state as? NSString)?.substring(from: state.characters.count - 2)