Don't forget that the loop() function repeats many times per second so the while loop will be entered many times per second and while a key is not pressed "HELLO" will be printed.
Under what circumstances do you want "HELLO" to be printed ?
Don't forget that the loop() function repeats many times per second so the while loop will be entered many times per second and while a key is not pressed "HELLO" will be printed.
Under what circumstances do you want "HELLO" to be printed ?