A string can have any value. LabVIEW cannot know what strings to expect at a case structure. So you have to type in the string you want in the title bar of the case structure. Also, with strings you need a default case to handle all strings that you didn't specify in other cases.
If you use integers, LabVIEW will create two cases to start with. You can edit the cases, for example you can create a case that handles the values 10..20. You'll still need a default case.
In one of your screenshots, you uses an enum. If you have kind of a state machine structure in your code, I recommend using enums (with type defs). Case structures know what cases to expect as the enums have fixed entries. With enums you don't need a default case (if you handle all enum values).
