All right, now that we know how to declare and initialize variables, we want to think about how we can build us an expressions. And so we're going to think about arithmetic operators. You've seen many of these in your past mathematical experience, so things like addition and subtraction and division are probably very familiar, right? These are binary operators that take two operands and produce a number, okay? The one for multiplication you know how to do multiplication, but you may not have seen this symbol use so we use the star for multiplication in computer science, okay? Again it's binary operation takes two operands produces one results, okay? Integer division I'm sure is new or maybe it's old, right, if you remember back to first grade, if I said three divided by two, you would say one with a remainder of one. So integer division gives me that one, well, maybe I'll make a better example, five divided by two, right? That's two with a remainder of one, so integer division is going to give me the two, okay? Mod is going to give me the one the remainder, so modulus is used to get the remainder. Integer divisions is used to get the whole number portion and we do this all the time in computer science, so these are really important, okay? Exponentiation is essentially like two squared or two cubed, we say two carat, and then whatever the exponent is. And then we have the unary operations of plus or minus, these are just signs, right? We typically only use the minus for a unary operation, but we could use a unary plus also, okay? All right, so we have to think about order of evaluation. Again, you've seen this in your past, you may have seen a simplified version but in math, you knew that multiplication division were done before addition and subtraction. And you knew that parentheses, changed the order of evaluation, so you do what's in parentheses first, okay? In computer science, we spell it out a lot better, so first we're going to go left to right, and we're going to do all the exponents. We evaluate those and then we move on to number two. We do all the positive and negative unary operations, then we move on to number three, where you do the multiplication and division. And then we move on to number four, we do the integer division, and then we move on to number five where we do the modules division. And lastly, we'll do addition and subtraction. And again, you can override the order evaluation using parentheses. So here are some examples of a couple different arithmetic expressions, these are pretty simple but I want to start you out slow. So I've got some integer arithmetic where I declare two integers, x and y, I initialize them to 10 and 8, and then I declare a variable named results and I set it to the addition of x and y, so it's 18 at the end, right? And then I'm going to do decimal arithmetic, where declare x and y as decimal, and x is going to be 10.1 and y is going to be 8.2 and then result is a decimal here and it's going to be 18.3 when I'm done. We also have what are called assignment operators and some of these are really too complicated to think about yet. But I introduced them so you can see them I'll talk about them slightly but then you don't have to think about them for a while. The one at the top is one we care about the straight assignment operator. Whatever is on the right hand side is assigned to what's on the left hand side we'll see an example in a second. The others are used for what I call accumulation. Essentially we've got a variable in an iteration, we're going to accumulate up a value by continually adding, subtracting, multiplying or dividing something to itself, okay? These are shorthand I'll show you examples of this later on when we get to iteration, okay? So here's an example of an assignment statement. Basically the syntax is the variable name is always in the left hand side and the right hand side is an expression. It could be a simple expression or a complicated expression. So here my variables my count in the example and my expression is really simple, it's the literal value 10. So it's going to take 10 and put it in the memory location that might count as that. All right, that's it for lesson one. So just a little bit of a review here integer data stores just whole numbers no decimal values, right? And integer division produces an integer type without a remainder. And declaring variable saves a memory location that we can reference later on in our code. And we can put values and expressions in that memory location and use them in our code. All right, I'll see you in the next lesson.
