PaulS:
pinMode(buttonPin, INPUT);So, tell us HOW the switch AND the external resistor (you MUST have one) are wired.
Or, use INPUT_PULLUP as the mode, and you won't need an external resistor.
int plus = stock +number;stock never changes. number never changes. You can push the switch until your finger falls off, and plus will ALWAYS be assigned the same value.
This is how it's connected. Note, the button works, when you press it the LCD starts showing the number, but it doesn't increase by pressing it again.
