Hi!
Firstly I think you should follow
this "consiglio" and try learn the basic first.
Secondly this type of problem haven't anything related with Ferduino code so should be asked in Arduino forum.
Thirdly you should read Arduino documentation before ask.
Look for this page:
https://www.arduino.cc/en/Tutorial/DigitalPinsNOTE: Digital pin 13 is harder to use as a digital input than the other digital pins because it has an LED and resistor attached to it that's soldered to the board on most boards. If you enable its internal 20k pull-up resistor, it will hang at around 1.7V instead of the expected 5V because the onboard LED and series resistor pull the voltage level down, meaning it always returns LOW. If you must use pin 13 as a digital input, set its pinMode() to INPUT and use an external pull down resistor.
Therefore this behaviour is expected on pin 13.
Best regards.