Value of type 'String' has no member 'stringByTrimmingCharactersInSet'

The new syntax is like this:

var cString = hex.trimmingCharacters(in: CharacterSet.whitespacesAndNewlines).uppercased()

As a suggestion, you don't need to specify that cString is a String, as this is assumed with the value you are assigning to it.

You can try this as well.

let trimmedString = hex.trimmingCharacters(in: CharacterSet.whitespaces)