>fillnumb will be =2
Why would it be? If fillnumb is 0, then that falls into your case 0, which sets fillnumb to 1. A break at the end of a case terminates the switch statement, so execution won't fall through to case 1.
root = tkinter.Tk()
buttons=[i for i in range(10)]
#If specific button is pressed, output "YES"
for num in buttons: