A switch works by comparing what is in switch() to every case.

switch (cnt) {
    case 1: ....
    case 2: ....
    case 3: ....
}

works like:

if (cnt == 1) ...
if (cnt == 2) ...
if (cnt == 3) ...

Therefore, you can’t have any logic in the case statements.

switch (cnt) {
    case (cnt >= 10 && cnt <= 20): ... } 

works like

 if (cnt == (cnt >= 10 && cnt <= 20)) ...

and that’s just nonsense.

Use if () { } else if () { } else { } instead.