Push Switch (S1) input point is at pin 9 of the Arduino. Connecting the display pins directly to Arduino I/O pins is not a good practice. For testing purpose only one 330 Ohm resistor (R2) is added ...

The LED segments of the display require current-limiting resistors when powered from a 5 V logic pin. The value of the resistor is typically between 330 and 470 ohms. ... Next is the Hookup diagram of ...