If your button is connected to ground like your comment says, then you need to define the pin as INPUT_PULLUP to enable the internal pullup on that pin or it will "float" when the button is not pressed which means it could read HIGH or LOW randomly.
If your button is connected to ground like your comment says, then you need to define the pin as INPUT_PULLUP to enable the internal pullup on that pin or it will "float" when the button is not pressed which means it could read HIGH or LOW randomly.