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It's also worth pointing out, and I mentioned this before,

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but I want to emphasize it again.

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That of course you are not limited to two numbers only

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when you perform a certain operation.

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It is perfectly fine to have

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an operation like this, for example.

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You can use as many values as you want in such operation.

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You can, of course also use floating point numbers.

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So decimal numbers here as well, by using a dot

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as a separator between the decimal place

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and the number in front of the decimal place,

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that's all possible.

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If you do use multiple values in your calculation though,

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as we do it here, and this is the result,

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then it is important to keep in mind

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that regular mathematical rules apply,

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which means that multiplication and division

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have a higher priority than using plus or minus.

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And then for here,

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this would be the first part that's evaluated.

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So we get 50 as a result,

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and then 50 would be deducted from ten plus three

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which is why we get -37 as a result.

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This might or might not be obvious, now it hopefully is.

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If you ever want to change these rules,

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you can do it just like you do it in regular math as well.

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You can add brackets, parentheses around the operation

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that should be evaluated first,

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because that now in turn has a higher priority

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then the regular priority.

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So now this term would be evaluated first

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and then the result of this term

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would be multiplied with ten.

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And that's why we now get a totally different result here.

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So that's what you should keep in mind

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about mathematical operations in your JavaScript code.

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Now, as I mentioned before,

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you can also store results of operations in variables.

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And I briefly want to come back to that.

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We can add a result variable,

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and we could store the result of this calculation

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in this variable.

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Or of any other calculation.

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Of course you can then also reassign the value.

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You can now store a new value in that variable,

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00:02:30,510 --> 00:02:33,600
and that can be any kind of value.

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For example, I could then store ten times four in result.

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Now I'm emphasizing this

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because there is one way of changing a variable

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that stores a value that can be shortened a little bit.

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And for that, let's say that for result,

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which has 40 after this line here,

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or which holds a value of 40 after this line.

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00:02:58,210 --> 00:03:01,260
We now want to add one to result.

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Now we can write it like this.

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This is perfectly fine JavaScript code.

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You can use a variable on the right side

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of such a variable assignment,

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even if you're assigning the result here,

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to the existing variable.

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Even if the variable you're assigning

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to is being used on the right side as well.

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This works because JavaScript will always evaluate

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and execute the right side of the equal sign first

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with the old value of result.

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So the value that is locked in, in line 13 so to say.

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And only once this calculation has been performed,

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the result of that calculation will be stored

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in that variable.

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So only then the variable value will change.

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That's why we can use a variable

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on the right side of the equal sign.

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Even if we're assigning to the very same variable.

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Now there are a couple of operations which are very common

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and therefore can be shortened, though.

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For example, if you add one to an existing variable.

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Then you can write it like this,

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or you can write it like this.

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This might look strange,

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but that is the same as saying

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00:04:18,320 --> 00:04:23,025
result equals result plus one, it's just a shorter form.

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We've got something similar for subtracting one.

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00:04:27,140 --> 00:04:29,653
Here we have result minus minus.

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00:04:31,380 --> 00:04:32,440
Now sometimes of course,

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00:04:32,440 --> 00:04:35,130
you don't just want to add or subtract one.

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Sometimes you maybe want to add five, let's say.

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In that case, you can't use the plus plus notation,

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but we still got a shorter version of writing this.

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You can write plus equals five,

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and this is equal to writing it like this.

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So whenever you use a variable

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on the right side of an equal sign

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and you then store the result in the very same variable,

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you can use shortcuts like this

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for simple mathematical operations.

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That also exists for minus, if you want to subtract

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and also for division and multiplication.

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00:05:15,030 --> 00:05:20,030
So we can also shorten these statements here, if we want to.

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This all works.

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00:05:24,720 --> 00:05:28,800
If I now console lock the result here at the bottom

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after changing it a couple of times,

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you will see that in that developer tools console,

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you've got a bunch of valid results

104
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from these lines of code that we added here.

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And these are just some shortcuts which can be useful

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if you're doing some mathematical operations

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and you are changing an existing variable

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based on its previous value.

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Now I will delete all of that for the moment,

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but these are a couple of shorthand notations

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that are worth keeping in mind.

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You will also encounter them again later in the course.