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When using multiple operators in one expression the order in which they are executed affects the resulting value.
Further Reading

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All the examples we've explored in our previous video give us a good idea of how

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to use basic math operations.

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But what happens when you want to go beyond basic math?

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What if you want to apply complex geometric, or algebraic formula?

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You're probably wondering what any of this has to do with building an app.

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Well, when you build an app, there's usually animation, for

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which you need to apply complex math.

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If you understand this stuff now, you will thank me later.

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So, back in Xcode, we're going to open a brand new playground.

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So go to File > New > Playground.

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And we're going to call this playground Operator Precedence.

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Because that's exactly what we're going to explore right now.

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Okay, so once again let's delete this var str.

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And 'm going to create variable x and

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assign it a whole series of calculations, so

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I'm just doing something random here so just bear with me.

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Now, I have practically all the operators here,

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I have addition, multiplication, subtraction, and remainder.

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So, in the results pane you can see that the value is 197.

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So, how did the system arrive at this conclusion?

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If we were calculating from left to right you

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would see that we would get a different value.

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So let's do that.

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Let's do 100 plus 100.

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That gives us 200.

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So, if we're going left to right, then we would do 200 minus 5, which is 195.

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And then 195 times 2, that gives us 390, right?

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Let's keep doing.

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So 390 divided by 3.

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That's 130.

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And then 130, remainder 7 gives us 4.

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But as you can see here, that the value is 197.

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And since we calculated from left to right, it gives us 4.

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So, what's going on here.

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Some operators take higher precedence than others.

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When the system looks at a line of code like ours, it knows which operations to

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perform first, and which operations to perform next.

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So multiplication, division, remainder, addition and subtraction.

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Swift assigns a priority, or precedence level to these operators.

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Precedence level 150 is given to multiplication, division, and remainder.

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Whereas precedence level 140,

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which is lower, is given to addition and subtraction.

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So, how does the system know which operators to execute when they

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have the same priority.

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It's actually quite simple.

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All these operators work from left to right.

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Let's try grouping them with parentheses so

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we can understand how this is calculated.

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Yes, that's right, you can always use parentheses if you simply want to

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understand the order of operations for yourself or for others.

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So let's find out how.

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So, since multiplication, division and

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addition have the same priority, which is higher than addition and subtraction.

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And it starts from left to right.

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That means that 5 times 2, because that's the first operation that's

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higher in precedence, is going to be executed.

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So that's 5 times 2, and then, if we're going left to right,

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there aren't any other higher precedence on the left of 5 times 2.

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So we have to move right.

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Then, after it multiplies 5 times 2, it's going to divide that number by 3.

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And then finally, it's going to

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divide that resulting value, or get the remainder of that resulting value by 7.

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And then it will perform the rest of the addition and subtraction.

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So, let's see if this actually works.

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We'll do 5 times 2, and we get 10.

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And then 10 divided by 3, we get 3.

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Then you have 3 remainder 7.

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Which is also equal to 3.

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And then finally you have 200 minus 3, which gives you 197.

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So there you go, now we understand how the system arrived at that number 197.

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I know you might be feeling a bit overwhelmed right now,

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because it is a lot of information.

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But, don't worry, because you don't need to memorize any of this.

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There are reference links in the notes section which you can bookmark and

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refer to them any time you want.

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A programmer's best friend is documentation.

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Not even the best programmers memorize it all.

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That's what documentation

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is for, you can go back

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to it anytime you want.

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