Okay.
I'm going to just jump right in and
hand simulate what's going on here.
These first three lines we just
declare three variables and
set them to initial values,
so I'm going to do that.
Okay, so
that's what that would look like.
And then here in display,
I'm saying display this arithmetic here.
Let's look and
see what the values of day 1, day 2, and
day 3 are at this point in the program.
Day 1 is 15.
Day 2 is 22 and day 3 is 18.
Now, this might seem a little bit silly
that I went off here to the side and
started keeping track
of these variables, but
as the programs get more complicated and
variables kind of change and
get modified in this space, it's really
important to be keeping track of things.
Anyways, the key insight for
this problem is that you're doing
both addition and a division here.
Now, if you remember from when Katherine
was talking about order of operation,
division always comes before addition.
Meaning the first thing that's going to
happen is this division right here.
So, 18 gets divided by 3, which is 6.
And then we have 15 plus 22 plus 6,
which equals 43.
So, it's going to print out 43.
So, is that correct?
Well, what we're trying to
do is find the average.
Finding the average involves
adding up all the numbers and
then dividing by the number
of numbers you have.
But we did the addition too early,
we do it before we've added
up these three numbers.
Really, it should be 15 plus 22
plus 18 then divided by three.
So 43 is not the correct answer.
And to make this code
do the correct thing,
you should be surrounding these
three variables with parentheses.
Then, you'll add 15 plus 22 plus 18.
And then divide it by 3, which will give
you the correct answer of about 18.3.