since a pin can be configured with an internal pullup resistor (INPUT_PULLUP) it's common to wire a switch between the pin and ground. the pullup makes the input HIGH. pressing the switch makes it LOW.
if you add an external pull-down resistor do you wire your switch between the pin and 5V?
with a pull-down and the following condition
the switch needs to be closed connecting the pin to 5V
don't understand how this can work with only the if condition. does it only work once?