Why do we use "-" in this video and not "-=" like we have learned?

Hi there,

In this example, we just want to evaluate the expression and return the result. So, return MAX_MISSES - misses.length(); evaluates to a number which we return out of the method. At the other end of that, the caller of the method probably assigns that value to something, probably another variable; I don't know.

So, the minus sign does maths and nothing else. It doesn't change any values of variables unless you assign it:

int cakes;
cakes = 5; 
// one gets eaten
cakes = cakes - 1;

Here, we evaluate the expression on the right of the = sign. It evaluates to 4, and we assign that back into cakes. So, cakes - 1 just creates a number which we assign into cakes (it could go anywhere) so that cakes now holds 4.

Shorthand for this is the -= operator. That deducts and assigns:

int cakes = 5;
cakes -= 1;

This has the same result; cakes now holds 4. So the -= operator evaluates and assigns. We don't need to do that in your initial example - we just want to calculate/evaluate the expression and use the number that generates. Indeed, you can't use this as you can't assign into a constant and MAX_MISSES -= misses.length(); doesn't generate a number that can be returned; it is a closed result as the assignment (if it were possible) swallows the evaluation, meaning there's nothing left to return.

I hope that makes sense!

Steve.