I would probably handle the score setting with a function. Something like this:
Then everytime you want to adjust the score you just call the function.
setScore(-5) \\ some kind of negative hit
setScore(5) \\ ate a power up bar or something....
That way you put all the logic and testing in one place. It makes it easier to maintain and adjust as you work out exactly what you want to do....
How do you display the score?
How do you want to display the score? Is it a graphic power bar or just a text readout?
In any event you put the code at the end of the function.